Semiconductor memory device

ABSTRACT

Conductive lines constituting word lines of memory cells and conductive lines constituting memory cell plate electrodes are formed in the same interconnecting layer in a memory device including a plurality of memory cells each including a capacitor for storing data in an electrical charge form. By forming the capacitors of the memory cells into a planar capacitor configuration, a step due to the capacitors is removed. Thus, a dynamic semiconductor memory device can be formed through CMOS process, and a dynamic semiconductor memory device suitable for merging with logic is achieved. Data of 1 bit is stored by two memory cells, and data can be reliably stored even if the capacitance value of the memory cell is reduced due to the planar type capacitor.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/922,936,filed on Aug. 23, 2004, now U.S. Pat. No. 7,046,543 which is acontinuation of application Ser. No. 10/119,094, filed on Apr. 10, 2002,now U.S. Pat. No. 6,785,157, which in turn claims the benefit ofJapanese Application No. 2001-151084, filed on May 21, 2001, JapaneseApplication No. 2001-208431, filed on Jul. 9, 2001, and JapaneseApplication No. 2001-294441, filed on Sep. 26, 2001, the disclosures ofwhich Applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor memory device, andparticularly to a semiconductor memory device having memory cellsstoring data in capacitors.

2. Description of the Background Art

In a data processing field and the like, a circuit device called asystem LSI (large-scale integrated circuit), wherein a memory device anda logic such as a processor are integrated in The same semiconductorchip, has been widely used in order to process data at a high speed withlow power consumption. In the system LSI, the logic and the memorydevice are interconnected through on-chip interconnect lines. Therefore,the system LSI has the following advantages: (1) since the load of thesignal interconnection lines is smaller than that of on-boardinterconnection lines, data/signals can be transmitted at a high speed;(2) since the number of pin terminals is not limited, the number of databits can be made large so that the band width in transmitting data canbe widened; (3) since the constituent elements are integrated on thesemiconductor chip, the system scale can be reduced to implement adown-sized and light system, as compared to the configuration whereindiscrete elements are arranged on a board; and (4) a macro prepared as alibrary can be arranged as a component formed on a semiconductor chip,and the efficiency of design is improved.

For the above-mentioned reasons, system LSIs are widely used in variousfields. As a memory device to be integrated in the system LSI, there areused a DRAM (dynamic random access memory), an SRAM (static randomaccess memory), and a flash type EEPROM (electrically erasable read onlymemory). As the logic, a processor for performing control andprocessing, an analogue processing circuit such as an A/D convertingcircuit, a logic circuit for performing a dedicated logic processing andsuch are used.

In the case that a processor and a memory device are integrated in asystem LSI, in order to reduce the number of manufacturing steps andcosts, these logic and memory device should be formed in the commonmanufacturing steps as long as possible. In a DRAM, data are stored inas capacitor in an electrical charge form. This capacitor haselectrodes, called a cell plate electrode and a storage node electrode,on a semiconductor substrate region. The structure of this capacitor hasa complicated shape, such as a hollow cylindrical shape, in order toreduce the occupancy area of the capacitor and to increase thecapacitance thereof as far as possible. With a DRAM and logic mixedprocess for forming a DRAM and a logic in the same manufacturing steps,transistors of the logic and those of the DRAM are formed in the samemanufacturing steps. However, it becomes necessary to carry out amanufacturing step for forming capacitors of the DRAM, and a flatteningstep for reducing a step height between the DRAM and the logic orbetween the memory array of the DRAM and the peripheral circuitrythereof, wherein the step height is caused based on thethree-dimensional structure of the capacitors of the DRAM. Thus,problems that the number of manufacturing steps increases significantlyand chip costs increases are caused.

In an SRAM, its memory cell is composed of 4 transistors and 2 loadelements. These load elements are usually formed of MOS transistors(insulated gate field effect transistors), but are not formed ofcapacitors or the like. Therefore, the SRAM can be formed through a fullCMOS logic process. That is, the SRAM and a logic can be formed in thesame manufacturing steps. An SRAM has been used, for example, for aregister file memory and a cache memory for a processor because of thehigh speed operability thereof and others.

In an SRAM, its memory cell is a flip-flop circuit. Thus, so far as apower supply voltage is supplied to the SRAM, data are held therein.Therefore, the SRAM does not require any refreshing for holding data,unlike a DRAM. Accordingly, the SRAM does not require any complicatedmemory control associated with the refreshing which is indispensable forthe DRAM. For the SRAM, therefore, control is made simpler than for theDRAM. Thus, the SRAM is widely used as a main memory in order tosimplify the system structure of a portable information terminal andsuch.

However, in portable information terminals, a larger quantity of datasuch as voice data and image data must be handled with a recentimprovement in functions thereof. Thus, a memory having a large memorycapacity is strongly required.

Concerning DRAM, the size thereof is being shrunk (is beingminiaturized) as the miniaturizing process is being developed. Forexample, in a 0.18-μm DRAM process, a cell size of 0.3 square μm isachieved. On the other hand, in SRAMs, their full CMOS memory cell iscomposed of 2 P channel MOS transistors and 4 N channel MOS transistors,that is, 6 MOS transistors as a whole. Even if the shrinking processadvances, it is necessary to isolate an N well for forming the P channelMOS transistors in a memory cell from a P well for forming the N channelMOS transistors thereof. Because of a restriction due to separationdistance between the wells and others, the shrinking of the memory sizein SRAMs advances less than in DRAM. For example, the memory size of anSRAM with a 0.18-μm CMOS logic process is about 7 square μm, and isabout 20 times greater than the memory size of DRAM. Thus, when an SRAMis used as a main memory having a large memory capacity, the size of thechip becomes very large. Accordingly, it is very difficult to merge anSRAM having a memory capacity of 4 M bits or more with a logic in asystem LSI having a restricted chip area.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor memorydevice having a small occupancy area and making it possible to achieve alarge memory capacity without increasing the number of manufacturingsteps significantly.

Another object of the present invention is to provide a semiconductormemory device which has an array configuration of a small occupancy areaand can be produced with a process similar to a CMOS process.

A further object of the present invention is to provide a semiconductormemory device having a memory cell configuration which has a smalloccupancy area and is suitable for a CMOS production process.

A still further object of the present invention is to provide asemiconductor memory device having a memory cell configuration which hasa small occupancy area and is based on DRAM cells.

A semiconductor memory device according to a first aspect of the presentinvention includes memory cells arranged in row and columns and eachincluding a capacitor having a cell plate electrode receiving areference voltage and a storage electrode for accumulating electriccharges according to storage data; and word lines arranged correspondingto the rows of memory cells and each connecting to the memory cell inthe corresponding row. These word lines are formed in the sameinterconnecting layer as the cell plate electrodes.

The semiconductor memory device according to the first aspect of thepresent invention further includes bit lines arranged corresponding tothe columns of memory cells, and each connecting to the memory cells inthe corresponding column; and a row selecting circuit for selecting anaddressed word line from the word lines in accordance with an addresssignal. The bit lines are arranged in pairs, and the memory cells arearranged such that data in the selected memory cells are simultaneouslyread out onto the bit lines in a pair by a selected word line.

A semiconductor memory device according to a second aspect of thepresent invention includes memory cells arranged in rows and columns.Each of the memory cells includes a capacitor having a cell plateelectrode receiving a reference voltage and a storage electrode foraccumulating electric charges according to storage data.

The semiconductor memory device according to the second aspect of thepresent invention further includes word lines arranged corresponding torows of the memory cells and each connecting to the memory cells on acorresponding row. These word lines include an interconnection lineformed as the same interconnecting layer of the cell plate electrode.The cell plate electrodes and the word lines are arranged in pairs.

The semiconductor memory device according to the second aspect of thepresent invention further includes a cell plate voltage control circuitfor changing the cell plate electrode voltage from this referencevoltage level after data are read out from the memory cell in an accessperiod of a memory cell, and returning the cell plate electrode voltageto the reference voltage level when the access cycle is completed.

A semiconductor memory device according to a third aspect of the presentinvention includes memory cells arranged in rows and columns. Each ofthe memory cells includes a capacitor having a cell plate electrodereceiving a reference voltage and a storage electrode for accumulatingelectric charges according to storage data.

The semiconductor memory device of the third aspect of the presentinvention further includes word lines arranged corresponding to the rowsof memory cells and each connecting to the memory cells on acorresponding row. Each of the word lines includes an interconnectionline formed in an interconnection layer lower than and different from aninterconnection layer of the cell plate electrodes.

The semiconductor memory device of the third aspect of the presentinvention further includes bit lines arranged corresponding to thecolumns of memory cells and each connecting to the memory cells in thecorresponding column. These bit lines are formed in a layer above theword lines and the cell plate electrodes. A contact is shared betweentwo memory cells aligned in the column direction, and the memory cellsadjacent in the row direction are simultaneously connected to thecorresponding bit lines. The memory cells connected to a pair of the bitlines adjacent to each other constitute a unit for storing1-bit data.

A semiconductor memory device according to a fourth aspect of thepresent invention includes memory cells arranged in rows and columns.Each of the memory cells includes a capacitor having a cell plateelectrode receiving a reference voltage and a storage electrode foraccumulating electric charges according to storage data.

The semiconductor memory device according to the fourth aspect of thepresent invention further includes word lines arranged corresponding tothe rows of memory cells and each connecting to the memory cells in thecorresponding row. Each of the word lines includes an interconnectionline formed in a lower first interconnection layer that is differentfrom an interconnecting layer of the cell plate electrodes. The cellplate electrodes include an interconnection line formed in a secondinterconnection layer above the first interconnection layer.

The semiconductor memory device according to the fourth aspect of thepresent invention further includes bit lines arranged corresponding tothe columns of memory cells and each connecting to the memory cells inthe corresponding column. Each of these bit lines is formed above theword lines and the cell plate electrodes. Units composed of two memorycells are arranged with one column shifted in the column direction, andthe bit lines constituting a pair sandwiches a bit line of another bitline pair. The memory cells of a unit are simultaneously connected tothe corresponding bit lines of a pair, and a 1-bit data is stored in thememory cells constituting a unit.

A semiconductor memory device according to a fifth aspect of the presentinvention includes memory cells arranged in row and columns. Each of thememory cells includes a capacitor having a cell plate electrodereceiving a reference voltage and a storage electrode for accumulatingelectric charges according to storage data, and the storage electrodelayer is formed facing to the cell plate electrode on a surface of asemiconductor substrate region.

The semiconductor memory device according to the fifth aspect of thepresent invention further includes word lines arranged corresponding tothe rows of memory cells and each connecting to the memory cells in thecorresponding row; and a cell plate voltage control circuit for changingthe voltage of the cell plate electrodes to a first reference voltagelevel in synchronization with the transition of a selected word lineinto a non-select state upon completion of an access cycle for selectinga memory cell, and changing the first reference voltage to a secondreference voltage level upon starting of the access cycle.

By forming the word lines connected to the memory cell rows and the cellplate electrodes of the memory cell capacitors at the sameinterconnecting layer, the projection of the memory capacitors in theupper direction from the substrate can be suppressed. That is, thethree-dimensional configuration of the capacitor section can be set intoa parallel plate type capacitor. Thus, a step based on the memory cellcapacitors can be reduced. Moreover, the word lines and the cell plateelectrodes of the memory cell capacitors can be formed by the samemanufacturing process. As a result, CMOS process can be used for themanufacturing process of the memory cells, and the memory cellcapacitors and the word lines can be formed through the samemanufacturing process as that of the logic.

Furthermore, it becomes unnecessary to use a flattening process(planarization process) step for reducing the step height between thelogic and the memory. Thus, the number of the manufacturing steps can bereduced.

Additionally, by using DRAM cells as the memory cells, memory cellshaving a small occupancy area can be achieved. Even in the configurationin which 1-bit data is stored in two DRAM cells, the area of the memorycell unit for storing the 1-bit data can be made far smaller as comparedto SRAM. Thus, a semiconductor memory device which has a small occupancyarea and is suitable for merging with a logic can be achieved.

By making the word lines and the cell plate electrodes at differentinterconnection layers, the facing area of each of the cell plateelectrodes and the corresponding storage node electrode can be madelarge. Consequently, the capacitance of the memory cells can be madelarge and a sufficiently large capacitance can be ensured againstshrinking of memory cells.

By changing the cell plate voltage dependently on an operation cycle, itis possible to compensate for a change in the voltage of the storagenode according to leakage current. Thus, data-holding characteristicscan be improved.

By making the memory cells into the trench isolation configuration andforming the cell plate electrodes, over the insulating film, on the sidewalls of the trenches, the so-called isolation merged type memory cellcapacitors can be realized. In memory cells subjected to shrinking,memory cell capacitors having a sufficiently large capacitance can beimplemented.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a layout of a memory cell array according toa first embodiment of the present invention;

FIG. 2 is a diagram schematically showing a cross sectional structure ofthe memory cell illustrated in FIG. 1;

FIG. 3 is a diagram showing connection among a memory cell, a senseamplifier and bit lines in the first embodiment of the presentinvention;

FIG. 4A is a graph showing the charge retention characteristics of thememory cell according to the first embodiment of the present invention,and FIG. 4B is a diagram showing an electrically equivalent circuit ofthe memory cells exhibiting the charge retention characteristics shownin FIG. 4A;

FIG. 5 is a diagram schematically showing the configuration of cellplate electrodes in the first embodiment of the present invention;

FIG. 6 is a diagram schematically showing the arrangement of the wholeof the cell plate electrodes in the first embodiment of the presentinvention;

FIG. 7 is a diagram showing a layout of a memory cell array in a secondembodiment of the present invention;

FIG. 8 is a diagram showing memory cell size and memory cell capacitorsize in the first and second embodiments of the present invention;

FIG. 9 is a diagram showing a layout of a memory cell array according toa third embodiment of the present invention;

FIG. 10 is a diagram showing an electrically equivalent circuit of thememory cells shown in FIG. 9;

FIG. 11 is a diagram schematically showing the configuration of thewhole of a semiconductor memory device according to the third embodimentof the present invention;

FIG. 12 is a diagram schematically showing the configuration of acentral control block shown in FIG. 11;

FIG. 13 is a diagram showing an example of the configuration of a latchcircuit shown in FIG. 12;

FIG. 14 is a diagram showing an example of the configuration of a rowrelated local control circuit shown in FIG. 12;

FIG. 15 is a diagram schematically showing the configuration of a memoryblock shown in FIG. 11;

FIG. 16 is a diagram showing the configuration of a sense amplifier banddesignating signal generating section in a row related local controlcircuit shown in FIG. 12;

FIG. 17 is a diagram showing correspondence relationship between memorycells and sense amplifiers in the third embodiment of the presentinvention;

FIG. 18 is a diagram showing connection between sense amplifiers in asense amplifier band shown in FIG. 17 and bit lines;

FIG. 19 is a diagram schematically showing correspondence relationshipbetween sense amplifiers and memory cells in a modification of the thirdembodiment of the present invention;

FIG. 20 is a diagram schematically showing connection between a senseamplifier in the arrangement shown in FIG. 19 and bit lines;

FIG. 21 is a diagram showing the configuration of a sense amplifiercontrol section in the row related local control circuit shown in FIG.12;

FIG. 22 is a diagram more specifically showing the configuration of thememory block and row related local control circuit of the semiconductormemory device in the third embodiment of the present invention;

FIG. 23 is a diagram schematically showing the configuration of amodification 2 of the third embodiment of the present invention;

FIG. 24 is a diagram schematically showing a layout of a memory cellarray according to a fourth embodiment of the present invention;

FIG. 25 is a diagram showing an electrically equivalent circuit ofmemory cells in the layout illustrated in FIG. 24;

FIG. 26 is a diagram schematically showing an arrangement of a senseamplifier band in the fourth embodiment of the present invention;

FIG. 27 is a diagram schematically showing a layout of a memory cellarray according to a fifth embodiment of the present invention;

FIG. 28 is a diagram showing an electrically equivalent circuit of thememory cells illustrated in FIG. 27;

FIG. 29 is a diagram schematically showing the configuration of thewhole of the semiconductor memory device in the fifth embodiment of thepresent invention;

FIG. 30 is a diagram schematically showing connection between main wordlines and substantial word lines in the fifth embodiment of the presentinvention;

FIG. 31A is a diagram schematically showing a layout of a memory cellarray according to a sixth embodiment of the present invention, and FIG.31B is a diagram showing a circuit that is electrically equivalent tothe layout illustrated in FIG. 31A;

FIG. 32 is a graph showing time dependent change of the voltages of astorage node and a cell plate node of the memory cell illustrated inFIGS. 31A and 31B;

FIG. 33 is a diagram schematically showing a layout of a memory cellarray according to a seventh embodiment of the present invention;

FIG. 34 is a diagram showing an electrically equivalent circuit of thelayout illustrated in FIG. 33;

FIG. 35 is a diagram schematically showing a cross sectional structureof a memory cell according to an eighth embodiment of the presentinvention;

FIG. 36 is a diagram showing signal waveforms upon reading out data ofthe memory cells illustrated in FIG. 35;

FIG. 37 is a diagram schematically showing the configuration of an arraysection of a semiconductor memory device according to a ninth embodimentof the present invention;

FIG. 38 is a diagram schematically showing a cross sectional structuretaken along line 37A-37B in FIG. 37;

FIG. 39 is a diagram schematically showing relationship between aninversion layer forming area and the interval between a sub word lineand a cell plate electrode;

FIG. 40 is a diagram schematically showing bit line read out voltage inthe configuration illustrated in FIG. 39;

FIG. 41 is a waveform diagram representing an operation of asemiconductor memory device according to the ninth embodiment of thepresent invention;

FIG. 42 is a diagram schematically showing a configuration of a mainportion of the semiconductor memory device according to the ninthembodiment of the present invention;

FIG. 43 is a diagram showing an example of the configuration of a cellplate driver showing in FIG. 42;

FIG. 44 is a diagram schematically showing an example of theconfiguration of a circuit for driving main cell plate lines illustratedin FIGS. 42 and 43;

FIG. 45 is a diagram schematically showing a modification of the maincell plate driving section;

FIG. 46 is a diagram schematically showing the configuration of a subword driver band of the semiconductor memory device according to theninth embodiment of the present invention;

FIG. 47 is a diagram showing a modification of the cell plate driver;

FIG. 48 is a diagram schematically showing a layout of a memory cellarray of a semiconductor memory device according to a tenth embodimentof the present invention;

FIG. 49 is a diagram schematically showing a cross sectional structuretaken along line 48A-48A in FIG. 48;

FIG. 50 is a diagram schematically showing a layout of a modification 1of the tenth embodiment of the present invention;

FIG. 51 is a diagram schematically showing a layout of a memory cellarray according to a modification 2 of the tenth embodiment of thepresent invention;

FIG. 52 is a diagram schematically showing the configuration of an arraysection of a semiconductor memory device according to an eleventhembodiment of the present invention;

FIG. 53 is a diagram schematically showing the arrangement of a cellplate electrode according to the eleventh embodiment of the presentinvention;

FIG. 54 is a diagram schematically showing a layout of an array sectionof a semiconductor memory device according to a twelfth embodiment ofthe present invention;

FIG. 55 is a diagram schematically showing a cross sectional structureof a memory cell according to a thirteenth embodiment of the presentinvention;

FIG. 56 is a diagram schematically showing the configuration of a memorycell array according to a fourteenth embodiment of the presentinvention;

FIG. 57 is a waveform diagram representing the operation of thesemiconductor memory device according to the fourteenth embodiment ofthe present invention;

FIG. 58 is a diagram schematically showing a cross sectional structureof the memory cell according to the fourteenth embodiment of the presentinvention;

FIG. 59 is a diagram schematically showing the configuration of a cellplate electrode driving section in the fourteenth embodiment of thepresent invention;

FIG. 60 is a waveform diagram representing the operation of a cell plateelectrode driver shown in FIG. 59;

FIG. 61 is a diagram schematically showing a modification of thefourteenth embodiment of the present invention;

FIG. 62 is a diagram schematically showing a layout of memory cellsaccording to a fifteenth embodiment of the present invention;

FIG. 63 is a diagram schematically showing a cross sectional structuretaken along line 62A-62A in FIG. 62;

FIG. 64 is a diagram schematically showing a cross sectional structuretaken along line 62B-62B in FIG. 62;

FIG. 65 is a diagram schematically showing a layout of a modification ofthe fifteenth embodiment of the present invention; and

FIG. 66 is a diagram schematically showing a cross sectional structuretaken along line 65A-65A in FIG. 65.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 1 is a diagram schematically showing the configuration of an arraysection of a semiconductor memory device according to a first embodimentof the present invention. A layout of memory cells arranged in 4 rowsand 2 columns is shown representatively in FIG. 1. In FIG. 1, word linesWL0-WL3 are arranged extending in the row direction. Cell plateelectrode lines CP0-CP2 are formed in the same interconnection layer asword lines WL0-WL3 and in parallel to these word lines. Accordingly,cell plate electrode lines CP0-CP2 are arranged such that adjacent cellplate lines sandwich two word lines, and are arranged extending in therow direction in the memory cell array. The cell plate electrode linesadjacent to each other in the column direction are separated from eachother by a word line WL arranged in between.

Word line WL0-WL3 are arranged corresponding to memory cell rows, andare connected to the memory cells in corresponding rows.

A constant reference voltage (cell plate voltage) is applied to each ofthe cell plate electrode lines.

Active areas AR for forming the memory cells are arranged in the columndirection in alignment with each other at predetermined intervals. Twomemory cells are formed in active area AR. Active area AR crosses twoword lines arranged adjacently to each other, and is arranged such thata part of the active area overlaps with the cell plate electrode in aplan view.

Bit lines BL0, /BL0, BL1 and /BL1 are arranged along the columndirection in alignment with active areas AR.

Contact CNT for connecting an active area to the bit line is providedbetween the adjacent word lines (word lines WL0 and WL1, or WL2 andWL3). In FIG. 1, through a contact CNT0, the active area of a memorycell MC0 is connected to a bit line BL0, and through contact CNT1, theactive area for forming a memory cell MC1 is connected to bit lines/BL0.

These memory cells MC (MC0 and MC1) have the configuration of a DRAMcell, as will be described in detail later. 1-bit data is stored bymemory cells MC0 and MC1. A set of the memory cells for storing 1-bitdata is referred to as a twin cell unit MU hereinafter.

Two bit lines are arranged in a pitch (arrangement interval) Lp of thememory cells in the row direction. The memory cell pitch is the distancebetween center lines of the active areas for forming memory cellsadjacent to each other in the row direction.

In the arrangement of the memory cells illustrated in FIG. 1, activearea AR is arranged in each row and each column. The memory cells isarranged at each crossing of rows and columns. This arrangement of thememory cells is called “closest packing cell arrangement”, and isusually used in an open bit line configuration, which is low in noiseimmunity. However, By arranging two bit lines in memory cell pitch Lp asillustrated in FIG. 1, it is possible to adopt a “folded bit lineconfiguration”, which is high in noise immunity, in the “closest packingcell arrangement”. In other words, by selecting the adjacent word lines(for example, word lines WL0 and WL2) with one word line interposed inbetween simultaneously, complementary data are read out onto bit linesBL0 and /BL0. By amplifying the data differentially, memory data in twincell unit TMU can be read out.

FIG. 2 is a diagram schematically showing a cross sectional structure ofeach of the memory cells in the memory cell arrangement illustrated inFIG. 1. In FIG. 2, memory cell MC includes impurity regions 2 a and 2 bformed, spaced from each other, on the surface of semiconductorsubstrate region 1, a conductive layer 3 formed, with a not-shown gateinsulating film interposed thereunder, on the surface of the regionbetween impurity regions 2 a and 2 b, a storage node region 4 connectedelectrically to impurity region 2 b, a conductive layer 5 arrangedfacing to storage node region 4, and a conductive layer 6 connectedelectrically to impurity region 2 a.

Conductive layer 3 constitutes a word line WL, conductive layer 5constitutes a cell plate electrode line CP, and conductive layer 6constitutes a bit line BL. Conductive layer 5 constituting the cellplate electrode is arranged facing the storage node electrode region ofthe adjacent memory cell across a cell isolation region 8. Storage noderegion 4 may be merely an inversion layer formed on the surface ofsemiconductor substrate region 1, or may be an impurity region intowhich an impurity is implanted and has an inversion layer formed on thesurface thereof.

The surface of a cell isolation film formed in cell isolation region 8is made flat, for example, by CMP (chemical mechanical polishing)process and is made to have substantially the same height as the surfaceof the substrate region, in order to make the step in the DRAM sectionas small as possible.

Conductive layers 3 and 5 are made in the same interconnection layerformed of silicon-containing materials, for example, polycrystal siliconinto which an impurity is implanted (doped polysilicon), polycides suchas tungsten silicide (WSix) or cobalt silicide (CoSix), or salicide(self-aligned silicide). Conductive layers 3 and 5 are formed in thesame interconnection layer as gate electrodes of transistors(transistors of the logic and peripheral transistors of the memorydevice) in a CMOS logic process. The wording “formed in the sameinterconnection layer” means “produced in the same manufacturing processstep”.

A gate insulating film and a capacitor insulating film are formed justunder conductive layers 3 and 5, respectively. These gate insulatingfilm and capacitor insulating film may be the same insulating filmformed in the same manufacturing step. The gate insulating film andcapacitor insulating film may be formed by oxide films different inthickness through a dual gate oxide film process. The “dual gate oxidefilm process” is a process in which two kinds of oxide films (insulatingfilms) different in thickness are formed through selective etching ofthe oxide films.

Conductive film 6 constituting bit line BL is made of a first metalinterconnection layer, and is formed above cell plate CP so that theso-called CUB (capacitor under bit line) configuration is achieved.

The memory cell capacitor has a planar type capacitor structure, and thestorage node electrode is formed of a storage node electrode layer madeof, for example, a diffusion layer at the surface of semiconductorsubstrate region 1, or an inversion layer formed at the surface ofsemiconductor substrate region 1. The cell plate electrode is formedextending in parallel to the word lines. Since the cell plate electrodeline and the word lines are formed in the same interconnection layerthrough the same manufacturing process step, it is unnecessary to addnew layers for the cell plate electrode and the storage node electrode.Thus, the manufacturing process can be made simple.

A step between the memory array section and the peripheral circuitsection is not produced because of the planar capacitor structure. Thus,it is unnecessary to introduce a flattening (planarization) process forreducing this step height, such as CMP (chemical mechanical polishing).Therefore, the memory array can be substantially formed through a CMOSlogic process, and the memory cell array can be formed in the samemanufacturing steps for forming the transistors of the logic.

When a row is selected, a row active command for directing row selectionis applied together with a row address. A (sub) word line pair with one(sub) word line interposed in between (see FIG. 1) is simultaneouslyselected by degenerating a second least significant bit (RA<1>), forexample, in the row address. For example, when word lines WL0 and WL2are simultaneously selected, memory cells MC0 and MC1 are connected tobit lines BL0 and /BL0, respectively.

Not-shown sense amplifiers are arranged corresponding to the bit linepairs. The sense amplifiers differentially amplify the voltages on thecorresponding bit line pairs. Accordingly, complementary data are storedin memory cells MC0 and MC1, that is, an H level data is stored in oneof the memory cells and an L level data is stored in the other memorycell. As a result, 1-bit data is stored in twin cell unit TMU.

FIG. 3 is a diagram showing an electrically equivalent circuit of thetwin cell unit. In FIG. 3, twin cell unit TMU includes two memory cellsMCa and MCb. Memory cell MCa is connected to a bit line BL, and memorycell MCb is connected to a bit line/BL. Each of memory cells MCa and MCbincludes a capacitor MS for storing data and an access transistor MTrendered conductive in response to a signal on the corresponding wordline and connects the capacitor MS to the corresponding bit line. Accesstransistor MT is formed of, for example, an N channel MOS transistor.

A sense amplifier SA for amplifying the voltages of bit lines BL and /BLdifferentially is provided for bit lines BL and /BL.

Upon accessing data, word lines WL0 and WL2 are simultaneously driveninto a select state. Responsively, the memory data in memory cell MCa isread out onto bit line BL, and the memory data in memory cell MCb isread out onto bit line /BL. Then, sense amplifier SA is activated toamplify differentially the voltages corresponding to the datatransferred onto bit lines BL and /BL.

A voltage (SN, H) and a voltage (SN, L) at the storage nodes of memorycells MC storing the H level data and the L level data are approximatelyrepresented by the following expressions:V(SN,H)≈Vbb+(VCCS−Vbb)·exp(−T/τa), andV(SN,L)≈Vbb·(1−exp(−T/τb).

Vbb is a negative voltage applied to the substrate region of the memorycells. Coefficients τa and τb each are a time constant decideddependently on a leakage current between the storage node and capacitorelectrode (cell plate electrode), a leakage current between the storagenode and the substrate region, an off leakage current of the memorycell-transistors, and others. When memory data in two memory cells areread out onto the bit line pair in a 1-bit/2-cell mode (twin cell mode)in which 1-bit data is stored in the two memory cells (DRAM cells), aread-out voltage difference ΔVb1 of the bit line pair is represented bythe following expression:ΔVb1=Cs·(V(SN,H)−V(SN,L))/(Cs+Cb),wherein Cs represents the capacitance of memory cell capacitor MS and Cbrepresents parasitic capacitance of each of bit lines BL and /BL.

FIG. 4A is a graph representing a simulation result of a relationship(that is, a relationship between the read-out voltage difference betweenthe bit line pair and data retention time) in a conventional DRAM celland the twin cell unit. In FIG. 4A, a vertical axis represents the bitline read-out voltage difference and a transverse axis represents thedata holding time.

In the DRAM cell (memory cell), the capacitance Cs of the memory cellcapacitor is 20 fF. On the other hand, for the twin cell unit, twocapacitors Cs each having a capacitance of 10 fF are used.

As shown in FIG. 4B, in a storage node SN(L) storing an L level data,there are a leakage current from the cell plate cell, a leakage currentto the substrate region, and a leakage current flowing through theaccess transistor to the corresponding bit line. On the other hand, in astorage node SN(H) storing an H level data, there are a leakage currentbetween the storage node and the cell plate electrode, a leakage currentto the substrate region, and a leakage current flowing through theaccess transistor to the corresponding bit line. A precharge voltage forthe bit line is 1 V.

In the case that simulation is performed under conditions of the leakagecurrents represented in FIG. 4B, the twin cell unit has a difference inread-out voltage ΔVb1 greater than that of the DRAM cell as thedata-holding time elapses. It can be understood that as the minimumvoltage difference (sense sensitivity) between the bit line pair whichthe sense amplifier can normally amplify differentially is smaller, thedata retention characteristics of the twin cell unit is better than thatof the DRAM cell. Therefore, in the case that the capacitance of thememory cell capacitor is smaller than the capacitance of the standardDRAM cell, the data retention characteristics can be reliably maintainedby storing data in the twin cell mode. Thus, it is possible to achieve amemory cell which occupies a small area and is superior in dataretention characteristics.

FIG. 5 is a diagram schematically showing the arrangement of the cellplate electrode lines in the first embodiment of the present invention.FIG. 5 shows an arrangement of the cell plate electrode lines for onememory sub array, which is an arrangement unit of sub word lines in ahierarchical word line configuration. A conductive layer 5 to be cellplate electrode lines CP and conductive layer 3 to be (sub) word linesare arranged, in the same interconnection layer, extending in the rowdirection and in parallel with each other. Sub word driver bands 12 aand 12 b including sub word drivers for driving the (sub) word lines arearranged at both sides of this memory sub array. It is supposed that theword lines are arranged in a hierarchical word line configuration of themain word lines and the sub word lines. The sub word lines will bereferred to as word lines hereinafter.

In sub word driver bands 12 a and 12 b, conductive lines 14 a and 14 bmade of the same first level interconnection layer as the conductivelayer 6 to be bit line BL, for example, are arranged. Each of conductivelayers 14 a and 14 b is connected through a contact 15 to cell plateelectrode conductive layer 5. Conductive layer 6 to be bit line BL isconnected to the sense amplifier included in a sense amplifier band 10.

By arranging conductive lines 14 a and 14 b for transmitting the cellplate voltage in sub word driver bands 12 a and 12 b, the cell platevoltage at a stable and necessary voltage level can be supplied even ifcell plate electrode lines CP are separated from each other in thecolumn direction in the memory cell array.

FIG. 6 is a diagram schematically showing the arrangement of the wholeof the cell plate electrode lines. In FIG. 6, a cell plate voltage line20 for transmitting the cell plate voltage from a cell plate voltagegenerating circuit 18 is provided along the outer circumference of amemory array MRY. Memory array MRY is divided into plural row blockRB0-RBm. Each of row blocks RB0-RBm is divided into plural memory subarrays SRY by the sub word driver bands. The arrangement of the cellplate lines is provided to memory sub arrays SRY, as shown in FIG. 5.

In the sense amplifier bands between row blocks RB0-RBm, cell platevoltage transmitting lines 22 are provided along the row direction. Inthe sub word driver bands between the memory sub arrays, cell platevoltage transmitting lines 21 are provided along the column direction.Cell plate voltage transmitting lines 20, 21 and 22 are interconnectedat crossings thereof. Cell plate voltage transmitting lines 21 and 22are connected to cell plate electrode lines CP in memory sub arrays SRY.

As shown in FIG. 6, the cell plate voltage transmitting lines arrangedin a meshed shape on memory array MRY are used to transmit the cellplate voltage from cell plate voltage generating circuit 18 to cellplate electrode lines CP inside the memory sub arrays SRY. The cellplate voltage can be stably supplied to cell plate electrode lines CParranged in the divided line configuration.

Cell plate voltage transmitting lines 21 and 22 arranged in memory arrayMRY may be formed in the same interconnecting layer as bit lines BL.

As described above, according to the first embodiment of the presentinvention, DRAM cells are used as memory cells, word lines and cellplate electrodes are formed in the same interconnection layer, andmemory cell capacitors having a planar capacitor configuration is usefor the memory cell capacitor. Thus, the following advantages areachieved: manufacturing process steps exclusively for forming a cellplate electrode layer become unnecessary; a step between a memory cellarray section and a peripheral circuit section can be reduced so thatprocess steps exclusively for reducing the step height becomeunnecessary; and the memory cell array section can be substantiallymanufactured according to a CMOS process. Thus, the memory cell arraycan be formed through the same process for manufacturing logictransistors.

Second Embodiment

FIG. 7 is a diagram schematically showing a layout of a memory arrayaccording to a second embodiment of the present invention. In the layoutillustrated in FIG. 7, active areas AR for forming memory cells arearranged in a staggered arrangement in the column direction such thatactive areas AR are shifted by ½ of pitch Lp of the memory cells in therow direction. The other configurations are the same as in the layoutillustrated in FIG. 1. Therefore, in the arrangement of the memory cellsillustrated in FIG. 7, with the two memory cells adjacent in the columndirection being one unit, and a plurality of the memory cell layoutunits are arranged in the column direction with the pitch of the one bitline deviated. Two bit lines BL (BL0-/BL1) are arranged in pitch LP inthe row direction of the memory cells.

Upon selecting memory cells, two word lines, for example, word lines WL0and WL2 are simultaneously selected. Storage data in a memory cell MC0is read out onto bit line BL0 through a contact CN0, and storage data ina memory cell MC1 is read out onto bit line /BL0 through a contact CNT1.Therefore, upon reading out data in the twin cell mode, bit lines BL0and/BL0 form a pair, and bit lines BL1 and /BL1 form a pair.Complementary data are read out onto the bit lines in a pair, and thevoltages on the bit lines in a pair are differentially amplified by thecorresponding sense amplifier. Thus, a folded bit line configuration canbe achieved.

In folded bit line configuration for the memory cells in a conventionalDRAM, the size ratio between length and width thereof is generally about2:1. An 8F2 cell having a width of 2 F and a length of 4 F is generallyadopted, wherein F is a value called a feature size (geometricaldimension) of design and is a value of a design standard (minimumdimension) plus a margin for overlap in a transfer step in aphotolithography process in the manufacturing of the memory cells, andothers.

FIG. 8 is a diagram showing the size of the memory cell in thearrangement of the memory cells as shown in FIG. 7. FIG. 8 illustratesthree active areas AR arranged in alignment in the row direction. Thedistance between active areas AR in the row direction is the featuresize F. Pitch LP in the row direction of memory cells MC is representedby Na·F. Active areas AR adjacent in the column direction are spacedapart from each other by the feature size F. The distance between oneend of cell plate electrode line CP and the end of active area AR is 0.5F.

The distance between bit line contact CNT and the other end of cellplate electrode line CP is represented by Nc·F, and the size of memorycell MC in the column direction is represented by Nb·F. In this case,the area Scap of a planar capacitor is represented by the followingexpression:Scap=(Na·F−F)·(Nb·F−Nc·F−0.5F)

The size (area) Scell of memory cell MC is represented by the followingexpression:Scell=Na·F·Nb·F

For the capacitor area Scap required for ensuring a capacitance Csnecessary for storing data stably, memory cell making the memory cellsize Scell minimum can be implemented by making the ratio between lengthand width (Nb:Na) sufficiently larger than 2:1 of conventional DRAM.

Even if pitch Lp of the memory cells in the word line direction issmall, bit line contacts CNT can be regularly formed on active areas ARby arranging active areas AR to be shifted by one bit line pitch asillustrated in FIG. 7. Thus, the bit line contacts can easily be laidout. In the case of the first embodiment, a contrivance of layout isnecessary in order to arrange the bit line contacts in active areas ARnarrow in the row direction since two bit lines are similarly arrangedin alignment with active areas AR.

Therefore, by arranging active areas AR in the column direction to beshifted by ½ of memory cell pitch Lp in the row direction in theconfiguration in which two bit lines are arranged between the pitches inthe row direction of the memory cells, the bit line contacts can beconstantly arranged in alignment with active areas AR. Thus, the bitline contacts can easily be laid out.

Third Embodiment

FIG. 9 is a diagram schematically showing a layout of a memory arrayaccording to a third embodiment of the present invention. The layout ofmemory cells illustrated in FIG. 9 is the same as the layout of thememory array illustrated in FIG. 7. In the configuration illustrated inFIG. 9, adjacent bit lines do not constitute a bit line pair. A bit linepair is provided by two bit lines with one bit line interposed inbetween. Upon selection of a word, one of word lines is selected.Therefore, memory cells MC0 and MC3 constitute a twin cell unit TMU, andmemory cells MC1 and MC4 constitute another twin cell unit. The otherconfigurations are the same as in FIG. 7. The same reference numeralsare allotted to the corresponding components, and detailed explanationthereof is omitted.

In the configuration as illustrated in FIG. 9, one of the word lines isselected, but two word lines do not need to be selected. Thus, currentconsumption can be reduced.

A bit line onto which no memory cell data is read out is arrangedbetween a bit line pair onto which memory cell data are read out.Therefore, by maintaining the bit line pair onto which no memory celldata are read (non-selected bit line pair) at a precharge voltage level,the bit lines of this non-select bit line pair can be used as shieldinginterconnect lines. Thus, capacitive coupling noise between bit linescan be suppressed further. Moreover, with memory cells each having a CUBconfiguration, the arrangement having an immunity (that is, resistanceagainst the above-mentioned capacitive coupling noise) which is as largeas that of a COB (capacitor over bit line) configuration, can beachieved.

FIG. 10 is a diagram schematically showing a main portion of the thirdembodiment of the present invention. In FIG. 10, a memory cell MCa isarranged corresponding to a crossing of a word line WL and a bit lineBLa, and a memory cell MCb is arranged corresponding to a crossing ofword line WL and a bit line /BLa. A bit line BLb is arranged between bitlines BLa and /BLa, and bit line /BLa is arranged between bit lines BLband /BLb. Bit lines BLa and /BLa are connected to a sense amplifier SAa,and bit lines BLb and /BLb are connected to a sense amplifier SAb. Senseamplifiers SAa and SAb are alternately arranged at both sides of the bitlines.

When word line WL is selected in the arrangement as shown in FIG. 10,data in memory cells MCa and MCb are read out onto bit lines BLa and/BLa. No memory cell data are read out onto lint lines BLb and /BLb. Inthis state, by a not shown bit line precharge/equalize circuit, bitlines BLb and /BLb are held at a predetermined precharge voltage leveland sense amplifier SAa is maintained in a non-active state. Senseamplifier SAa is activated to amplify data in a twin cell unit TMUcomposed of memory cells MCa and MCb.

FIG. 11 is a diagram schematically showing the configuration of thewhole of a semiconductor memory device according to the third embodimentof the present invention. In FIG. 11, a memory array is divided intoplural memory blocks MB0-MBn. Each of memory blocks MB0-MBn includesmemory cells arranged in rows and columns, sense amplifiers, a sub worddriver band in which sub word drivers for selecting a sub word line arearranged. Blocks MB0-MBn are divided into banks BNK0-BNK3 for eachpredetermined number of the blocks. In a backbone band BBD, row localcontrol circuits LRK0-LRKn are arranged corresponding to memory blocksMB0-MBn, respectively. A main control signal and a bank designatingsignal from central control block MCK are transmitted through backboneband BBD to row local control circuits LRK0-LRKn.

In FIG. 11, the signals transmitted through backbone band BBD fromcentral control block MCK, include bank designating signals BKLT0-BKLT3,a block selecting signal BS for selecting a memory block in each of thebanks, a pre-decoded signal MWX for selecting a main word line, and asub word line pre-decoded signal SWX for selecting a sub word line.Other row related control signals, such as a main sense amplifieractivating signal for activating a sense amplifier, are generated fromcentral control block MCK and transmitted through backbone band BBD.

When a command related to row selection is externally supplied tocentral control block MCK, a main control signal and block selectingsignal BS for selecting a row is generated. In this case, in centralcontrol block MCK, other row related control signals, such as the senseamplifier activating signal, are generated for the individual banks inaccordance with a bank address for designating a selected bank.

In the arrangement as shown in FIG. 11, row local control circuitsLRK0-LRKn are selectively activated in accordance with the row relatedcontrol signals and block selecting signal BS for individual banks fromcentral control block MCK, so as to perform operation related to rowselection in a corresponding memory block.

FIG. 12 is a diagram schematically showing the configuration of centralcontrol block MCK as shown in FIG. 11. In FIG. 12, central control blockMCK includes a command decoder 30 for decoding a command CMD forinstructing an operation mode and generating an operation modeinstructing signal in accordance with the decode result, a main rowrelated control circuit 32 for generating a control signal related torow selection in accordance with the operation mode instructing signalfrom command decoder 30, a bank decoder 33 activated in accordance withan output signal from main row related control circuit 32 to decode abank address signal BAD, a block decoder 34 activated in accordance withthe output signal from main row control circuit 32 to decode a blockaddress signal BLAD for generating block selecting signals BS<k:0>, apre-decoder 35 activated under control of the output signals from mainrow control circuit 32 to pre-decode a word line address signal WAD andgenerate pre-decode signals MWX (=X<19:4>) for selecting a main wordline and pre-decode signals SWX (=X<3:0>) for selecting a sub word line,and a latch circuit 36 for latching an output from bank decoder 33 inaccordance with the output signal from main row related control circuit32 to generate bank designating signals BKLT<3:0>.

Latch circuit 36 includes latch circuits (flip-flop) arrangedcorresponding to banks BNK0-BNK3, and holds a bank designating signalBKLTi in an active state during the time when the corresponding bank isselected.

Main row related control circuit 32 also generates a row related controlsignal for each bank in accordance with the output signal from commanddecoder 30. Pre-decode signals X<19:4> (=MWX) outputted from pre-decoder35 is divided into groups each having a predetermined number ofpre-decode signals. In accordance with a pre-decode signal from each ofthe groups, a main word line out of 256 main words is designated. Inaccordance with pre-decode signals X<3:0> (=SWX), one sub word line outof four sub word lines is selected. In other words, a 4-way hierarchicalword line configuration, in which 4 sub word lines are arranged for onemain word line, is employed in memory blocks MB0-MBn.

FIG. 13 is a diagram showing an example of the configuration of latchcircuit 36 as shown in FIG. 12. FIG. 13 shows the configuration of alatch circuit for a bank BNKi. In FIG. 13, latch circuit 36 includes anAND circuit 36 a which receives a row activation instructing signal RACTand a bank designating signal BASi from bank decoder 33 shown in FIG.12, an AND circuit 36 b which receives bank designating signal BASi anda precharge instructing signal PRG, and a flip-flop 36 c which is set inresponse to a rise of an output signal from AND circuit 36 a and isreset in response to a rise of an output signal from AND circuit 36 b.Bank designating signal BKLTi is outputted from an output Q of flip-flop36 c.

When a row active command instructing selection of a row is applied, rowactivation instructing signal RACT is outputted from command decoder 30shown in FIG. 12. When the precharge command for setting a bank into aprecharge state is applied, precharge instructing signal PGR isoutputted from command decoder 30 shown in FIG. 12. Therefore, bankdesignating signal BKLTi is kept in a select state during the time whenbank BNKi is in a row selecting state.

FIG. 14 is a diagram schematically showing the configuration of portionsrelated to word line selection in the row local control circuit. In FIG.14, the configuration of a row local control circuit LRKj for a memoryblock MBj is representatively shown. Memory block MBj is included inbank BNKi.

In FIG. 14, row local control circuit LRKj includes an inverter 40receiving latch bank designating signal BKLTi, a L level latch circuit42 for latching pre-decode signals X<19:4> in accordance with an outputsignal from inverter 40 and latch bank designating signal BKLTi, a levellatch circuit 43 for latching a block selecting signal BS<j> in responseto latch bank designating signal BKLTi and the output signal frominverter 40 to generate a latch block selecting signal BSLTj, and alevel latch circuit 44 for latching pre-decode signals X<3:0> inaccordance with latch bank designating signal BKTLi and the outputsignal from inverter 40 to generate a latch pre-decode signal XLT<3:0>.Latch circuits 42, 43 and 44 have the same configuration, and in FIG.14, reference numerals are attached only to components of latch circuit42.

Level latch circuit 42 includes a transmission gate 45 renderedconductive in response to latch bank designating signal BKLTi and theoutput signal from inverter 40, and an inverter latch 46 for latchingpre-decode signals X<19:4> supplied through transmission gate 45.Inverter latch 46 generates latch pre-decode signals XLT<19:4>.

Furthermore, row local control circuit LRKj includes a main row decoder47 for decoding latch pre-decoding signals XLT<19:4> and transmitting amain word line driving signal ZMWL on main word line MWL in accordancewith a word line activating timing signal RXTi, an inverter 48 receivinglatch block selecting signal BSLTj, an AND circuit 49 receiving wordline activating timing signal RXTi, the output signal from inverter 48and latch pre-decode signals XLT<3:0>, a level shifter 50 for convertingthe level of the output signal from AND circuit 49 to generate subdecode fast signals ZSDF<3:0>, and a sub decoder 51 receiving the outputsignal from level shifter 50 to generate complementary sub decodesignals SD<3:0> and ZSD<3:0>.

Level shifter 50 converts a signal of an amplitude at a peripheral powersupply voltage level VCC to a signal of an amplitude at a high voltagelevel VPP higher than an array power supply voltage VCCS. Sub decoder 51receives sub decode fast signals ZSDF<3:0> having amplitude VPP fromlevel shifter 50 to generate sub decode signals SD<3:0> having amplitudeVPP and complementary sub decoding signals ZSD<3:0> having amplitudeVCCS. When a corresponding sub word line is selected, sub decode signalSD turns into an H level (i.e., a high level) of high voltage level VPPand a complementary sub decode signal ZSD turns into an L level (i.e., alow level). Sub decode signals SD<3:0> are generated by inverting subdecode fast signals ZSDF<3:0>.

Word line activating timing signal RXTi attains an H level of theperipheral power supply voltage level when selected, and is suppliedfrom central control block MCK as shown in FIG. 11 to bank BNKi.

When latch bank designating signal BKLTi attains an H level, or a selectstate, in row local control circuit LRKj shown in FIG. 14, transmissiongate 45 is rendered non-conductive in each of level latch circuits 42-44and level latch circuits 42-44 enter a latching state. When memory blockMBj corresponding to row local control circuit LRKj is selected, latchblock selecting signal BSLTj attains L level of a select state. On theother hand, when the corresponding memory block MBj is in a non-selectstate, latch block selecting signal BSLTj is at H level.

When latch block selecting signal BSLTj is in the non-select state, theoutput signal from inverter 48 is at L level and the output signal fromAND circuit 49 is at L level. Thus, all sub decode fast signalsZSDF<3:0> from level shifter 50 are kept in a non-select state (at Hlevel). On the other hand, when latch block selecting signal BSLTj is inthe select state, the output signal from inverter 48 attains H level.Moreover, AND circuit 49 supplies latch pre-decode signals XLT<3:0> tolevel shifter 50 in accordance with word line activating timing signalRXTi.

Level shifter 50 converts the level of latch pre-decode signals XLT<3:0>to generate sub decode fast signals ZSDF<3:0>. One of latch pre-decodesignals XLT<3:0> is in a select state and the other latch pre-decodesignals XLT<3:0> are in a non-select state. The voltage level of thenon-selected latch pre-decode signals is transitions to high voltagelevel VPP and the selected latch pre-decode signal is driven into Llevel. Therefore, one of sub decode fast signals ZSD<3:0> is in a selectstate (at L level).

When word line activating timing signal RXTi is activated at apredetermined timing, main word line driving signal ZMVL from main rowdecoder 47 is driven in accordance with the decoding result. AND circuit49 is enabled so that output signals thereof are changed in accordancewith latch pre-decode signals XLT<3:0>. A sub word line corresponding toan addressed row is driven into a select state in accordance with subdecode signals SD<3:0> and ZSD<3:0> from sub decoder 51 and main wordline driving signal ZMWL from main row decoder 47.

When BNKi is in a non-select state, latch bank designating signal BKLTiis at L level of a non-select state and all of level latch circuits42-44 are in a conductive state. By transmitting block selecting signalsBS<k:0> from central control block MCK to row local control circuitsLRKn-LRK0 through backbone band BBD, latch block selecting signal BKLTjis already in a definite state at a decode timing of main row decoder 47and sub decoder 51. Thus, word line selecting operation can be performedat a faster timing.

Pre-decode signals X<19:4> are generated from row address bits RA<9:2>,and pre-decode signals X<3:0> are generated from row address bitsRA<1:0>. Block selecting signal BS<j> is generated from the row addressof an appropriate bit number, dependently on the number of memoryblocks.

FIG. 15 is a diagram schematically showing the configuration of aportion related to one main word line MWL. As shown in FIG. 15, four subword lines SWL0-SWL3 are provided for main word line MWL. Respective subword lines SWL0-SWL3 are driven into a select state in accordance with amain word line driving signal on main word line MWL and sub decodesignals SD<3:0> and ZSD<3:0> by sub word drivers SWD0-SWD3. Sets of subdecode signals SD0 and ZSD0 to SD3 and ZSD3 are applied to sub worddrivers SWD0-SWD3, respectively.

Memory cells MC are arranged corresponding to crossings between sub wordlines SL0 and SWL1, and bit lines BL0 and /BL0. Memory cells MC are alsoarranged corresponding to crossings between sub word lines SWL2 andSWL3, and bit lines BL1 and /BL1. Therefore, if a sub word line to beselected can be specified, the sense amplifier to be activated can bespecified. Since non-selected bit line pairs can be specified, with thebit lines of the non-selected bit line pairs used as shieldinginterconnection lines, sensing operation can be performed easily byholding bit line precharging/equalizing circuits provided to thenon-selected bit line pairs in an active state.

The number of the sense amplifiers performing the sense operation isreduced to half times, so that sensing current can also be reduced tohalf times. Thus, a semiconductor memory device which is low in currentconsumption and is superior in noise immunity can be achieved.

Sub decoders 51 shown in FIG. 14 are arranged in crossings of sub worddriver bands where sub word drivers SWD are arranged and sense amplifierbands where the sense amplifiers are arranged, corresponding to therespective sub word driver bands. Only sub decode fast signals ZSDF<3:0>are transmitted to the sense amplifier bands. Thus, according to thepresent configuration, the number of interconnection lines can be madesmaller than in the configuration in which complementary sub decodingsignals SD<3:0> and ZSD<3:0> are transmitted through sense amplifierbands. Through one sub decoder, the sub decode signals are transmittedto the sub word drivers arranged in the corresponding sub word driverband, and therefore, the sub word decode signals are transmitted at ahigh speed to drive a corresponding sub word line into a select state.

FIG. 16 is a diagram showing an example of the configuration of a senseamplifier control section of row local control circuit LRKj. In FIG. 16,row local control circuit LRKj includes a composite gate 52 receivinglatch pre-decoding signals XLT<0> and XLT<1> and latch block selectingsignal BSLTj, an inverter 53 for inverting an output signal fromcomposite gate 52 to generate an upper side sense amplifier banddesignating signal BSLUj, a composite gate 54 receiving latch pre-decodesignals XLT<2> and XLT<3> and latch block selecting signal BSLTj, and aninverter 55 for inverting an output signal from composite gate 54 togenerate a lower side sense amplifier band designating signal BSLLj.

Composite gates 52 and 54 have the same configuration, and only thelatch pre-decode signals applied thereto are different. In FIG. 16,reference numerals are attached to components of composite gate 52.Composite gate 52 equivalently includes an OR circuit 52 a whichreceives latch pre-decode signals XLT<0> and XLT<1>, and a NAND circuit52 b which receives output signals from the OR circuit and latch blockselecting signal BSLTj.

When either latch pre-decode signal XLT<0> or XLT<1> is driven into aselect state, one of sub word lines SWL0 and SWL1 is driven into aselect state. When either latch pre-decode signals XLT<2> or XLT<3> isdriven into a select state, one of sub word lines SWL2 and SWL3 isdriven into a select state. The shown configuration is a hierarchicalword line configuration, and therefore, the terms of “main” word linesand “sub” word lines are used in order to distinguish main/sub wordlines. Latch pre-decode signals XLT<0>-XLT<3> correspond to sub wordline SWL0-SWL3, respectively.

FIG. 17 is a diagram schematically representing correspondingrelationship between a selected sub word line and sense amplifiers. InFIG. 7, a sense amplifier band SABj+1 is arranged between row blocks RBjand RBj+1, and a sense amplifier band SABj is arranged above row blockRBj. These sense amplifier bands have sense amplifiers arranged in theconfiguration of an alternate arrangement type. The sense amplifiers arealternately arranged at both sides of the corresponding row block in thesense amplifier bands.

When sub word line SWL0 or SWL1 is selected in row block RBj, sensingoperation is performed by upper side sense amplifier band SABj. In thisstate, all of the sense amplifiers included in sense amplifier bandSABj+1 are kept in a non-active state. When sub word line SWL2 or SWL3is selected in row block RBj, sensing operation is performed by lowerside sense amplifier band SABj+1 and the sense amplifiers included insense amplifier band SABj are kept in a non-active state.

In the same way, when sub word line SWL0 or SWL1 is selected in rowblock RBj+1, sensing operation is performed by upper side senseamplifier band SABj+1 and the sense amplifiers included in a not shownlower side sense amplifier band are kept in a non-active state. When subword line SWL2 or SWL3 is selected in row block RBj+1, sensing operationis performed by the sense amplifiers in a not shown sense amplifier bandbelow row block RBj+1.

Therefore, in any of the row blocks, the position of the senseamplifiers which perform sensing operation is determined uniquely,dependently on the position of a selected sub word line. Thus, theactivation of the sense amplifiers can easily be controlled.

FIG. 18 is a diagram showing connection between one sense amplifier andbit lines. As shown in FIG. 17, in sense amplifier band SABj+1, senseamplifier SA performs sense operation on memory cells on sub word lineSWL2 or SWL3 in row block RBj. On the other hand, in row block RBj+1,sense amplifier SA performs sense operation on memory cells on sub wordline SWL0 or SWL1. As shown in FIG. 18, therefore, different bit linesare connected to the same sense amplifier SA between the adjacent rowblocks. Specifically, sense amplifier SA is electrically connected tobit lines BLL1 and /BLL1 in one row block of the adjacent row blocks,and is electrically connected to bit lines BLR0 and /BLR0 in the otherrow block. Bit lines BLL0 and /BLL0 are connected to a not shown senseamplifier. In the same way, bit lines BLR1 and /BLR1 are connected toanother not shown sense amplifier.

As shown in FIG. 18, the bit lines connected to sense amplifier SA aredifferent every row block. However, sense amplifier SA is arrangedcorresponding to four bit lines in each sense amplifier band SAB (SABj,SABj+1). Different bit lines in adjacent row blocks can easily beconnected electrically to the same sense amplifier SA.

The bit lines selected according to a column address are different foreach row block. However, the position of a memory cell is designated onthe basis of a bank address, a block address, a row address, and acolumn address, and therefore, no problem concerning external dataaccess is caused.

Upon column selection, one of the sense amplifiers in the senseamplifier bands is selected in accordance with a column selectingsignal. It is sufficient to select a column select gate provided for anactivated sense amplifier band upon column selection. In the case that acolumn decoder is arranged in alignment with a row decoder correspondingto each row block, it is merely required to enable a column decoderarranged corresponding to an activated amplifier band in accordance withthe block address.

In the case that a column decoder is arranged in common to a pluralityof the row blocks, it is required to apply a signal of the logicalproduct of a sense amplifier activating signal and a column selectingsignal to a column selecting gate for selecting a column. Alternatively,a local IO line arranged corresponding to the row blocks are connectedto a global IO line provided in common to the row blocks in accordancewith a block selecting signal. Page size is equivalently ½ times of thepage size of a conventional DRAM array arrangement. Therefore, even ifthe positions of the bit lines connected to a sense amplifier aredifferent, the column addresses of the associated bit lines can be madethe same by doubling a column selecting signal, that is, by assigningthe same column address to the adjacent bit line pairs. Thus, it ispossible to perform correctly a column selection on the activated senseamplifiers.

[Modification]

FIG. 19 is a diagram schematically showing the configuration of amodification of the third embodiment of the present invention. In FIG.19, sub word lines SWL0-AWL1023 are mirror-symmetrically arranged in rowblocks RBj and RBj+1. Specifically, in row block RBj, sub word linesSWL0-SWL1023 are arranged in this order from sense amplifier band SABjat the upper side thereof towards sense amplifier band SABj+1 at thelower side thereof. On the other hand, in row block RBj+1, sub wordlines SWL1023-SWL0 are arranged in this order from sense amplifier bandSABj+1 at the upper side thereof towards a not shown sense amplifierband at the lower side thereof.

Corresponding to the mirror symmetrical arrangement of memory cells inrow blocks RBj and RBj+1, signals to main row decoders and sub decodersare mirror-symmetrically arranged. When sub word line SWL0 or SWL1 isdesignated in accordance with latch pre-decode signals XLT<1:0> in rowblock RBj, and sensing operation is performed by sense amplifier bandSABj. On the other hand, when sub word line SWL1022 or SWL1023 (SWL2 orSWL3) is designated in accordance with latch pre-decode signals XLT<3:2>in row block RBj, sensing operation is performed by sense amplifier bandSABj+1 at the lower side.

Therefore, in the case that one of latch pre-decode signals XLT<1:0> isselected in row block RBj, sense amplifier band identifying signal BSLUjis activated in the configuration shown in FIG. 16. On the other hand,in the case that one of latch pre-decode signals XLT<3:2> is selected,sense amplifier band identifying signal BSLLj is activated. In row blockRBj+1, the arrangement thereof is mirror-symmetrical, and therefore,when one of latch pre-decode signals SLT<1:0> is selected, senseamplifier band identifying signal BSLLj is activated, and when one oflatch pre-decode signals XLT<3:2> is selected, sense amplifier bandidentifying signal BSLUj is activated.

In this way, bits lines in the same column are connected to the samesense amplifier SA as shown in FIG. 20. According to a selected wordline (sub word line), the corresponding sense amplifier band can beactivated correctly. In FIG. 20, bit lines BLL1 and /BLL1 in one ofadjacent row blocks are connected to sense amplifier SA, and bit linesBLR1 and /BLR1 in the other row block are connected to the same senseamplifier SA. Bit lines BLL0 and /BLL0 are connected to a not shownsense amplifier, and bit lines BLR0 and /BLR0 are also connected to anot shown sense amplifier.

Thus, according to the shown configuration, the bit lines on the samecolumn in the adjacent row blocks are electrically connected to the samesense amplifier SA. As for a column address, therefore, a columnselecting gate connected to sense amplifier SA can be selected on thebasis of the same column selecting signal.

In this configuration, a column decoder may be arranged in alignmentwith a row decoder and arranged for each row block, or may be arrangedin common to the row blocks.

FIG. 21 is a diagram showing the configuration of a sense amplifiercontrol section in the row local control circuit. In FIG. 21, a rowlocal control circuit LRKj−1 is provided for sense amplifier band SABj,and a row local control circuit LRKj is provided for sense amplifierband SABj+1. Row blocks RBj−1 and RBj share sense amplifier band SABj,and row block RBj and a not shown row block RBj+1 share sense amplifierband SABj+1.

Row local control circuit LRKj−1 includes an OR circuit 60 whichreceives sense amplifier band identifying signals BSLLj−1 and BSLUj, andan AND circuit 61 which receives output signals from OR circuit 60 and amain sense amplifier activating signal SOMi. A sense amplifieractivating signal SOEj is supplied from AND circuit 61 to the senseamplifiers in sense amplifier band SABj.

Row local control circuit LRKj includes an OR circuit 62 which receivessense amplifier band identifying signals BSLLj and BSLUj+1, and an ANDcircuit 61 which receives output signals from OR circuit 62 and mainsense amplifier activating signal SOMi. AND circuit 63 outputs a senseamplifier activating signal SOEj+1 for sense amplifier band SABj+1.

When a row is selected in row block RBj, one of sense amplifieridentifying signals BSLUj and BSLLj is activated in row local controlcircuit LRKj. Therefore, when main sense amplifier activating signalSOMi is activated, one of sense amplifier activating signals SOEj andSOEj+1 from AND circuits 61 and 63 is activated so that one of senseamplifier bands SABj and SABj+1 is activated.

Main sense amplifier activating signal SOMi is a signal generated fromcentral control block MCK shown in FIG. 11 to a selected bank BNKi.

FIG. 22 is a diagram more specifically showing the configuration of therow local control circuit. FIG. 22 shows the configuration of the rowlocal control circuit for three row blocks RBa, RBb, and RBc. In FIG.22, in row block RBa a bit line precharge/equalize circuit BPEa isprovided to bit lines BLLa and /BLLa. Bit lines BLLa and /BLLa areconnected to a sense amplifier SAa through a bit line isolating gateBIGLa.

In row block RBb, bit lines BLa and /BLa are connected to senseamplifier SAa through a bit line isolating gate BIGUb and bit lines BLband /BLb are connected to a sense amplifier SAb through a bit lineisolating gate BIGLb. A bit line precharge/equalize circuit BPEUb isprovided to bit lines BLa and /BLa. A bit line precharge/equalizecircuit BPELb is provided to bit lines BLb and /BLb.

In row block RBc, bit lines BLRb and /BLRb are connected to senseamplifier SAb through a bit line isolating gate BIGUc. A bit lineprecharge/equalize circuit BPEUc is provided to bit lines BLRb and/BLRb.

When a sub word line SWLa is selected in row block RBb, data in memorycells MC are read out onto bit lines BLa and /BLa. When a sub word lineSWLb is selected, the data in memory cells MC are read out onto bitlines BLb and /BLb.

An equalization instructing signal BEQLa to a bit lineprecharge/equalize circuit BPEa is outputted from a NAND circuit 70which in turn receives latch bank designating signal BKLTi and a senseamplifier band identifying signal BSLLa. An isolation instructing signalBLILa to bit line isolating gate BIGLa is outputted from a NAND circuit71 which receives latch bank designating signal BKLTi and a senseamplifier band identifying signal BSLUb. NAND circuit 71 has a levelconverting function of converting a signal at a level of peripheralpower supply voltage VCC to a signal of high voltage level VPP.

A sense amplifier activating signal SOEa to sense amplifier SAa isgenerated from a combination of an OR circuit 72 which receives senseamplifier band designating signals BSLLa and BSLUb and a NAND circuit 73which receives an output signal from OR circuit 72 and main senseamplifier activating signal SOMi.

An isolation instructing signal BLIUb to a bit line isolating gate BIGUbis generated from a NAND circuit 74 which receives sense amplifier banddesignating signal BSLLa and latch bank designating signal BKLTi. ThisNAND circuit 74 also has a level converting function of converting asignal at a level of peripheral power supply voltage VCC to a signal ofhigh voltage level VPP.

An equalization instructing signal BEQUb to bit line precharge/equalizecircuit BPEUb is generated from a NAND circuit 75 which receives senseamplifier band identifying signal BSLUb and latch bank designatingsignal BKLTi.

An equalization instructing signal BEQLb to bit line precharge/equalizecircuit BPELb is generated from a NAND circuit 76 which receives senseamplifier band identifying signal BSLLb and latch band designatingsignal BKLTi.

An isolation instructing signal BLILb to bit line isolating gate BIGLbis generated from a NAND circuit 77 which receives latch bankdesignating signal BKLTi and a sense amplifier band identifying signalBSLUc. This NAND circuit 77 also has a level converting function ofconverting a signal of the peripheral power supply voltage level to asignal of the high voltage level.

A sense amplifier activating signal SOEb to sense amplifier SAb isgenerated from a combination of an OR circuit 78 which receives senseamplifier band identifying signals BSLLb and BSLUc and an AND circuit 79which receives an output signal from OR circuit 78 and main senseamplifier activating signal SOMi.

An isolation instructing signal BLIUc to bit line isolating gate BIGUcis generated from a NAND circuit 80 which receives sense amplifier bandidentifying signal BSLLb and latch bank designating signal BKLTi.

An equalization instructing signal BEQUc to a bit lineprecharge/equalize circuit BPEUc is generated from a NAND circuit 81which receives latch bank designating signal BKLTi and a sense amplifierband identifying signal BSLUc.

Each of NAND circuits 70, 75, 76 and 81 which generate bit lineequalization instructing signals may have a level converting functionand generate bit line precharge/equalize instructing signals at the highvoltage level.

In the configuration shown in FIG. 22, sense amplifier band identifyingsignal BSLLa indicates that the sense amplifier band including senseamplifier SAa is used when row block RBb is selected. Sense amplifierband identifying signal BSLUb indicates that row block RBb is selectedand sense operation is performed by the sense amplifier band includingsense amplifier SAa. Sense amplifier band identifying signal BSLLbindicates that row block RBb is selected and sense operation isperformed by the sense amplifier band including sense amplifier SAb.Sense amplifier band identifying signal BSLUc indicates that row blockRBc is selected and sense operation is performed by the sense amplifierband including sense amplifier SBb.

It is now assumed that sub word line SWLa is selected in row block RBb.Since memory cell data are read out onto bit lines BLa and /BLa in thisstate, sense operation is performed by sense amplifier SAa. In thiscase, therefore, sense amplifier band identifying signal BSLUb attains Hlevel and the other sense amplifier band identifying signals BSLLa,BSLLb and BSLLc are at L level of an inactive state. Equalizationinstruction signal BEQUb from NAND circuit 75 turns L level so that bitline precharge/equalize circuit BPEUb enters an inactive state.

On the other hand, NAND circuit 74 holds isolation instructing signalBLIUb at H level of the high voltage level, since sense amplifier bandidentifying signal BSLLa is at L level, or in a non-select state. On theother hand, since latch bank designating signal BKLTi is activated, NANDcircuit 71 drives isolation instructing signal BLILa into L level whensense amplifier band identifying signal BSLUb turns H level.Responsively, bit line isolating gate BIGLa is made nonconductive. Senseamplifier SAa is isolated from bit lines BLLa and /BLLa while bit linesBLa and /BLa are connected to sense amplifier SAa.

NAND circuit 70 holds equalize instructing signal BEQLa at H level sincesense amplifier band identifying signal BSLLa is at L level, or in anon-select state. Therefore, bit line precharge/equalize circuit BPEacontinuously precharges and equalizes bit lines BLLa and /BLLa.

On the other hand, equalization instructing signal BEQLb is kept at Hlevel since sense amplifier band identifying signal BSLLb is at L level.Therefore, bit lines BLb and /BLb are continuously precharged by bitline precharge/equalize circuit BPELb. Since sense amplifier bandidentifying signal BSLUc is at L level, isolation instructing signalBLILb is kept at H level of the high voltage level so that bit lineisolating gate BIGLb is kept in a conductive state. In the same way,NAND circuit 80 holds isolation instructing signal BLIUc at H level ofthe high voltage level since sense amplifier band identifying signalBSLLb is at L level. Therefore, bit line isolating gate BIGUc is kept ina conductive state.

Furthermore, NAND circuit 81 holds equalization instructing signal BEQUcat H level since sense amplifier band identifying signal BSLUc is at Llevel. Therefore, bit lines BLRb and /BLRb are continuously prechargedand equalized by bit line precharge/equalize circuit BPEUc.

In this state, sense amplifier activating signal SOEa is activated inaccordance with main sense amplifier activating signal SOMi so that datais sensed, amplified and latched by sense amplifier SAa. At this time,bit line precharge/equalize circuit BPELb is kept in an active state andthe voltage level of bit lines BLb and /BLb is fixed to the level ofprecharge voltage to function as shielding interconnection lines.

By utilizing the configuration of the row local control circuit as shownin FIG. 22, only the bit line pair sharing a sense amplifier with thebit line pair onto which memory cell data are read out, is isolated fromthe corresponding sense amplifier and sensing operation is performed onthe memory cell.

In the configuration of the bit lines and the memory cells as shown inFIG. 22, the bit lines in the same column may be connected to the samesense amplifier, or the bit line pairs on the columns shifted from eachother by one column may share the sense amplifier.

[Modification Example]

FIG. 23 is a diagram schematically showing the configuration of amodification of the third embodiment of the present invention. In FIG.23, a bank A sense amplifier band SABA is arranged at one side, in thecolumn direction, of a row block RBA, and a bank B sense amplifier SABBis arranged between row blocks RBA and RBB. Memory cells arranged at thecrossing of a bit line pair BLPa and a sub word line SWLA in row blockRBA are connected to a sense amplifier in bank A sense amplifier bandSABA. On the other hand, in row block RBA, data in memory cells arrangedcorresponding to the crossing of a sub word line SWLB and a bit linepair BLPb are sensed and amplified by bank B sense amplifier band SABB.

A local control circuit 85 is provided to bank A sense amplifier bandSABA, and a local control circuit 86 is provided to bank B senseamplifier band SABB. A latch bank designating signal BSLTA and a latchblock selecting signal BSA specifying memory blocks sharing bank A senseamplifier band SABA are supplied to local control circuit 85. A latchbank designating signal BSLPB designating a bank B and a block selectingsignal BSB specifying memory blocks sharing bank B sense amplifier bandSABB are supplied to local control circuit 86.

By supplying bank designating signals BSLTA and BSLTB to local controlcircuits 85 and 86 as shown in FIG. 23, a single row block RBA can bedivided into two banks. Thus, a semiconductor memory device of amulti-bank configuration can easily be achieved.

In this configuration of local control circuits 85 and 86, the blockselecting signals are used, instead of sense amplifier band identifyingsignals BSLLa, BSLUb, BSLLb and BSLUc used in the configuration of thelocal control circuit shown in FIG. 22, to control the circuits relatedto sensing operation in accordance with the block selecting signals andthe latch bank designating signal specifying the corresponding bank.

Even if a non-hierarchical word line configuration is used as word lineconfiguration, the same technical advantages can be obtained.

As described above, according to the third embodiment of the presentinvention, each bit line pair is arranged with a bit line of another bitline pair interposed in between. Thus, data can be read out and writtenin a twin cell mode by selecting a word line. The number of the senseamplifiers to be activated at a time can be halved so that currentconsumption can be reduced.

Fourth Embodiment

FIG. 24 is a diagram schematically showing a layout of a memory cellarray according to a fourth embodiment of the present invention. In FIG.24, active areas AR are arranged in alignment along the columndirection. In each active area AR, 2-bit memory cells adjacent in thecolumn direction are formed similarly to the third embodiment. Bit linesBL0 and /BL0 are arranged along the column direction in alignment withactive areas AR. Therefore, one bit line is arranged at the pitch of thememory cells in the row direction. Thus, the pitch condition on the bitlines can be relaxed.

A memory cell MC0 is connected to a bit line BL0 through a contact CNT,and a memory cell MC2 is connected to a bit line /BL0 through a contact.When a word line WL1 is selected, data in memory cells MC0 and MC2 areread out onto bit lines BL0 and /BL0, respectively. Accordingly, in thecase that data are stored in the twin cell mode, a twin cell unit isprovided by memory cells MC0 and MC2.

Cell plate electrode lines CP0-CP2 are formed in the sameinterconnection layer as word lines WL0-WL3 similarly to the first tothird embodiments.

FIG. 25 is a diagram representing connection between memory cells andbit lines according to the fourth embodiment of the present invention.In the case that data in the twin cell mode are stored, a twin cell unitTMU is provided by memory cells MC0 and MC2. Memory cell MC0 isconnected to a bit line BL, and memory cell MC2 is connected to a bitline /BL. These bit lines BL and /BL in a pair are arranged such that abit line is arranged at a pitch of the memory cells in the rowdirection. Therefore, pitch condition along the row direction on a senseamplifier SA is relaxed. As a result, sense amplifier SA can be arrangedwith sufficient margin.

FIG. 26 is a diagram schematically showing the configuration of an arraysection in the semiconductor memory device according to the fourthembodiment of the present invention. FIG. 26 representatively shows fourrow blocks RB0-RB3. A bit line pair BLP is arranged in each of rowblocks RB0-RB3. The pitch condition on bit lines BL and /BL whichconstitute bit line pair BLP is sufficiently mitigated. Therefore, in asense amplifier band SAB0 shared between row blocks RB0 and RB1. senseamplifiers SA are arranged corresponding to the bit line pairs BLPincluded in row blocks RB0 and RB1. No sense amplifier band is arrangedbetween row blocks RB1 and RB2. A sense amplifier band SAB1 is arrangedbetween row blocks RB2 and RB3. In this sense amplifier band SAB1, senseamplifiers are arranged corresponding to bit line pairs included in rowblocks RB2 and RB3.

Consequently, it is unnecessary to arrange alternately sense amplifiersat both sides of a row block as is generally seen in conventional DRAM.Thus, the number of the sense amplifiers can be halved so that arrayarea can be reduced.

In the configuration of the memory cells according to the fourthembodiment, adjacent bit lines are arranged in a pair and all of thememory cells in one row are selected through selection of a word line.

As described above, according to the fourth embodiment of the presentinvention, the bit lines are arranged in alignment with the active areasso that the pitch conditions, in the row direction, of the bit lines canbe mitigated. Thus, the sense amplifiers can be arranged with sufficientmargin. As a result, in each of the sense amplifier bands, the senseamplifiers can be provided to all of the bit line pairs in acorresponding row block. Thus, the number of the sense amplifier bandscan be reduced so that the area of the memory array can be reduced.

Fifth Embodiment

FIG. 27 is a diagram schematically showing a layout of an array sectionof a semiconductor memory device according to a fifth embodiment of thepresent invention. In FIG. 27, active areas AR are arranged extendingcontinuously in the column direction. With two bit lines provided foreach of these active areas AR, the bit lines are arranged extending inthe column direction in alignment with active areas AR.

Similarly to the above-mentioned embodiments, cell plate electrode linesCP0-CP2 and word lines WL are formed in the same interconnection layerin the row direction.

In the layout illustrated in FIG. 27, active areas AR are continuouslyextends in the column direction, and DRAM cells sharing a cell plateelectrode line share a capacitor. Thus, each of unit memory cells MC4and MC5 is formed in an area surrounded by contacts at both sides ofcell plate electrode CP1. At both sides of each of the contacts, wordlines WL0 b and WL1 a, or word lines WL1 b and WL2 a are arrangedcorresponding to different ports. Each unit memory cell MC has a2-transistor/1-capacitor configuration.

Adjacent bit lines are bit lines associated with different ports. InFIG. 27, bit lines BLa, BLb, /BLa, and /BLb are repeatedly andsuccessively arranged in this order. Upon storing data in the twin cellmode, the data are stored in unit memory cells MC4 and MC5 of a 2-porttwin cell unit PTMU. For example, when word line WL1 a is selected, datain memory cells MC4 and MC5 are read out onto bit lines BLa and /BLa. Onthe other hand, when word line WL1 b is selected, the memory data inmemory cells MC4 and MC5 are read out onto bit lines BLb and /BLb.Therefore, by constructing a 2-port cell having a2-transistor/1-capacitor configuration as a unit memory cell and furtherby using two unit memory cells to store complementary data, the data canbe stored in the twin cell mode.

FIG. 28 is a diagram showing an electrically equivalent circuit of thelayout illustrated in FIG. 27. In FIG. 28, 2-port twin cell unit PTMU isformed of two unit cells MC4 and MC5. Since unit cells MC4 and MC5 havethe same configuration, reference numerals are attached to onlycomponents of unit cell MC4 in FIG. 28. Unit cell MC4 includes acapacitor CT, an access transistor TR1 for connecting capacitor CT tobit line BLa in response to a signal on word line WL1 a, and an accesstransistor TR2 for connecting capacitor CT to bit line BLb in responseto a signal on word line WL1 b.

A sense amplifier SAPA for a port A is provided to bit lines BLa and/BLa, and a sense amplifier SAPB for a port B is provided to bit linesBLb and /BLb.

When word line WL1 a is selected, memory data in 2-port twin cell PTMUare read out onto bit lines BLa and/BLa. The memory data are amplifiedand latched by sense amplifier SAPA. When word line WL1 b is driven intoa select state in this arrangement, the memory data in 2-port twin cellunit PTMU are read out onto bit lines BLb and BLb, amplified and latchedby sense amplifier SAPB for port B. Accordingly, sense amplifiers SAPAand SAPB can be accessed through different ports A and B.

Sense amplifier SAPA for port A is connected to a read port for readingout data, and sense amplifier SAPB for port B is connected to a writeport for writing data. Thus, data can be written and read out throughthe different ports. In the present embodiment, therefore, access timecan be made far shorter than in the configuration in which data arewritten and read through one port in a time division multiplexed manner.

FIG. 29 is a diagram schematically showing the configuration of thewhole of the semiconductor memory device in the fifth embodiment of thepresent invention. In the configuration shown in FIG. 29, the port A isused as a data reading port and the port B is used as a data writingport.

The memory array shown in FIG. 29 is divided into row blocks RB0-RBn.Read port sense amplifier bands RPSB and write port sense amplifierbands WPSB are alternately arranged in areas between row blocks RB0-RBnand in areas outside of the memory array in the column direction. InFIG. 29, read port sense amplifier bands RPSB0-RPSBk and write portsense amplifier bands WPSB0-WPSBk are arranged, where k is n/2. Withrespect to each of the row blocks, the read port sense amplifier bandand the write port sense amplifier band are arranged oppositely to eachother.

Local control circuits LCCT0-LCCTn are arranged corresponding to rowblocks RB0-RBn. Each of local control circuits LCCT0-LCCTn isselectively activated, under control by a read port control circuit RCTLand a write port control circuit WTCTL, to select a memory cell andactivate the sense amplifiers in the corresponding sense amplifier band.

In order to arbitrate the conflict of data writing and data reading outon the same address, an arbitrating circuit ABTR is provided. When datawriting and data reading out are simultaneously performed on the sameaddress, arbitrating circuit ABTR carries out such an arbitration ascausing the data reading out faster. When the same row is accessed bythe port A and the port B and the word line in the same address issimultaneously selected, charged voltage of the capacitors in the 2-porttwin cell unit are simultaneously read out onto a port A bit line and aport B bit line. Therefore, bit line readout voltage is dispersed sothat the advantages of the twin cell mode may be damaged. Accordingly,it is necessary to prohibit simultaneous access by the different portsto the same row. The simultaneous access to the same row address isarbitrated by arbitrating circuit ABTR.

In the arbitration of the access conflict, the timing of internaloperation is controlled such that writing operation from the write portis started after sensing operation of the sense amplifiers in the readport completes. This timing control is achieved, for example, by makingvalid a sense operation completion indicating signal (corresponding to acolumn lock signal in a standard DRAM) of the read port at the time ofdetecting the access conflict and then delaying an access of the writeport.

Read port sense amplifier bands RPSB0-RPSBk are connected to a datareadout circuit DRH through a read out data bus RDDB, and write portsense amplifier bands WPSB0-WPSBk are connected to a data write circuitDWK through a write data bus WRDB. Read port sense amplifier bandsRPSB0-RPSBk are connected to read bit line pairs BLPR in thecorresponding row blocks, and write port sense amplifier bandsWPSB0-WPSBk are connected to write bit line pairs BLPW in thecorresponding row blocks. In row blocks RB0-RBn, therefore, read portsense amplifier bands RPSB0-RPSBk have a shared sense amplifierconfiguration, in which read bit line pairs BLPR in adjacent row blocksshare the sense amplifier band, and the write port sense amplifier bandsWPSB0-WPSBk−1 also have a shared sense amplifier configuration, in whichwrite bit line pairs BLPW in adjacent row blocks share the senseamplifier band.

Therefore, each of local control circuits LCCT0-LCCTn performs the samecontrol for connection of a bit line pair and a sense amplifier as donein the conventional shared sense amplifier configuration. Specifically,when read port control circuit RPCTL controls data readout operation inaccordance with a command instructing an operation mode, under thecontrol of the read port local control circuit included in local controlcircuits LCCT0-LCCTn, read bit line pairs BLPR in a selected row blockare connected to the corresponding read port sense amplifier band RPSBand the read bit line pairs in the row block sharing the sense amplifierband with this selected row block is isolated from the correspondingread port sense amplifier band. In the other row blocks, they are notselected, and all of their read bit line pairs are kept in a prechargedstate. After the isolation of the bit lines is completed, a read portrow decoder provided for the selected row block is activated to select arow.

Consequently, as the configuration of the local control circuits, thesame configuration as that shown in FIG. 22 can be used even in such a2-port configuration. It is sufficient merely to control the connectionof the sense amplifier band and the row block and the activation of thesense amplifier band in accordance with block selecting signals(including port information) generated under the control of read portcontrol circuit RPCTL and write port control circuit WPCTL, instead ofsense amplifier band identifying signals BSLL and BSLU.

Upon word line selection, a read port row decoder and a write port rowdecoder are provided for the row blocks and the row decodercorresponding to a selected port is activated through the control byread port control circuit RPCTL and write port control circuit WPCTL.Thus, a desired word line can be selected.

Arbitrating circuit ABTR merely performs arbitration for preventing datafrom being destructed by write data before reading out the data, and canbe constructed by ordinary arbitrating circuit.

The sequence of the access to the 2-port memory may be decided by aspecification. The arbitration upon occurrence of access conflict may beperformed by an external controller.

In the case that read access and write access are alternately orselectively performed in the configuration in FIG. 29, the write portbit line pair arranged between the read port bit line pairs is kept at apredetermined voltage level by the corresponding bit lineprecharge/equalize circuit when the read port is accessed. When thewrite port is accessed, the read port bit line pair between the bit linepairs for this write port is kept at the predetermined precharge voltagelevel by the corresponding precharge/equalize circuit.

When both of a read port word line and a write port word line are keptin a selected state, the read port word line is first driven into aselect state and subsequently the write port word line is driven into aselect state, or vice versa. The voltage levels of the bit lines of theport accessing earlier are latched by the corresponding senseamplifiers. In this case, the bit lines having the voltage levelslatched function as shielding interconnection lines for the bit linesfor the other port selected later.

In either case, therefore, the bit lines adjacent to each other functionas shielding bit lines. Thus, using the memory cells having the CUBconfiguration that memory cell capacitors are formed under the bitlines, an array configuration having an immunity against bit line noiseis equivalent to that of memory cells having a COB configuration can beachieved.

The active areas for forming memory transistors are linearly andcontinuously extended in the column direction, and are not projected inthe row direction. Thus, the active areas can be arranged at a highdensity in the row direction.

In the configuration shown in FIG. 29, port A is used as a read port andport B is used as a write port. Each of ports A and B may be used as aport for inputting and outputting data. By writing and reading out datathrough different ports, the data writing and the data reading can beperformed in parallel so that data access can be made at higher speed.

FIG. 30 is a diagram schematically showing an example of the arrangementof word lines in the fifth embodiment of the present invention. In FIG.30, Port A sub word lines SWL0 a-SWL3 a are provided to a port A mainword line MWLa, and port B sub word lines SWL0 b-SWL3 b are provided toa port B main word line MWLb. Therefore, a 4-way hierarchical word lineconfiguration is employed for each of ports A and B. Port A sub wordlines SWL0 a-SWL3 a and port B sub word lines SWL0 b-SWL3 b arealternately arranged in the column direction. A sub word driver SWDa isprovided for each of read port sub word lines SWL0 a-SWL3 b, and a subword driver SWDb is provided for each of B port sub word lines SWL0b-SWL3 b.

These sub word drivers SWDa and SWDb are alternately arranged in a subword driver band. Therefore, even if the interval between the sub wordlines is small, sub word drivers SWDa and SWDb can be arranged withsufficient margin.

In this configuration, the word lines may be an 8-way hierarchical wordline configuration, and may be a non-hierarchical word lineconfiguration in which eight sub word lines are provided for a main wordline.

As described above, according to the fifth embodiment of the presentinvention, the active areas are linearly extended and the cell plateelectrodes and the word lines are formed in the same interconnectionlayer. Thus, 2-port memory which operate in the twin cell mode caneasily be achieved. Between each bit line pair, a bit line for adifferent port is arranged so that the bit line interposed in betweencan be used as a shielding bit line. As a result, a memory arrayconfiguration which is superior in noise immunity can be achieved.

Sixth Embodiment

FIG. 31A is a diagram schematically showing a layout of a memory cellarray according to a sixth embodiment of the present invention. In FIG.31A, active areas AR for making 2-bit DRAM cells arranged in alignmentin the column direction are arranged in alignment in the columndirection. Bit lines BT (BL0, /BL0) are arranged at a pitch of memorycells in the row direction. Word lines WL (WL0-WL3) and cell plateelectrode lines CP are formed in the same interconnecting layer. In thesixth embodiment, the cell plate electrode lines are divided for eachtwin cell unit TMU, which is a memory unit in the twin cell mode. Thatis, a cell plate electrode line CPa is provided in common to memorycells (DRAM cells) MC6 and MC7 in FIG. 31A. This cell plate electrodeline CPa is isolated from cell plate electrodes CP of DRAM cells in theother twin cell units. This relation holds for the other cell plateelectrode lines CPb-CPd. Additionally, these cell plate electrode linesCPa-CPd, and CP are kept in an electrically floating state.

FIG. 31B is a diagram showing an electrically equivalent circuit of twincell unit TMU shown in FIG. 31A. In FIG. 31B, a DRAM cell (memory cell)MC6 includes a capacitor MQ and an access transistor TQ. The capacitorsof memory cells MC6 and MC7 are connected in series between storagenodes SNa and SNb of memory cells MC6 and MC7. Therefore, a cell platenode CPN is kept at a voltage level obtained by capacitance division ofthe voltages of storage nodes SNa and SNb.

It is assumed that an H level data is written in storage node SNa and anL level data is written in storage node SNb, as shown in 32. In thiscase, cell plate node CPN is at a voltage level of the intermediatevoltage level (VCCS/2). When the voltage level of storage node SNa islowered with the passage of time by storage node to substrate leakagecurrent, the voltage drop of storage node SNa is transmitted to cellplate node CPN through capacitive coupling. Then, the voltage drop istransmitted to storage node SNb. Consequently, the voltage level ofstorage node SNb is also lowered with the voltage drop of storage nodeSNa.

Thus, a difference Va between the voltages of storage nodes SNa and SNbis constant even if time passes. Accordingly, a voltage differencecaused between bit lines BL0 and /BL0 upon selecting twin cell unit TMUis constant even if leakage current is generated. As a result, thevoltage difference (readout voltage) caused between bit lines BL0 and/BL0 can be constant. In principle, data can be stably stored and can beread out for sensing operation until the storage node SNb and thesubstrate region are forward biased. Even if the voltage levels ofstorage nodes SNa and SNb are lowered by leakage current, the voltagelevels of storage nodes SNa and SNb can be recovered to original H leveland L level by selecting twin cell unit TMU and operating thecorresponding sense amplifier.

Therefore, by dividing the cell plate electrode lines for each twin cellunit and keeping the cell plate lines in an electrically floating state,a semiconductor memory device with excellent data retentioncharacteristics can be achieved.

Seventh Embodiment

FIG. 33 is a diagram schematically showing a layout of a memory cellarray according to a seventh embodiment of the present invention. In thelayout illustrated in FIG. 33, active areas AR for making 2-bit DRAMcells are arranged in alignment in the column direction and are isolatedfrom each other. Cell plate electrode lines CP0-CP2 and word linesWL0-WL3 are formed in the same interconnection layer. Cell plateelectrode lines CP0-CP3 may be a formed into a division configuration ormay be arranged extending in the row direction.

Conductive lines 101 a, 102 a, 102 b and 101 b are arranged in alignmentwith active areas AR. Conductive lines 101 a and 102 b are arranged inalignment with in the column direction, and conductive lines 102 a and101 b are arranged in alignment in the column direction.

In a region above a cell plate electrode line CP1, for example, by meansof a second level metal interconnection layer 100, conductive line 101 ais connected to conductive line 101 b through via holes 104 a and 104 b.In a region above cell plate electrode line CP1, by means of ainterconnection line 103 which is at the same layer as conductive lines102 a and 102 b, conductive line 102 a is interconnected to conductiveline 102 b so as to cross the second level metal interconnection layer(crossing interconnection line) 100. Conductive lines 101 a and 101 bconstitute bit line /BL0, and conductive lines 102 a and 102 bconstitute the bit line BL0.

Bit lines BL0 and /BL0 have a cross section on cell plate electrode lineCP1, and the positions thereof are exchanged. The configuration in whichthe positions of these bit lines are exchanged in the cross section iscalled a so-called “twisted bit line” configuration, and makes itpossible to reduce the capacitive coupling between the bit lines.Moreover, by superimposing the common phase noise onto the bit linesadjacent to each other, the bit line to bit line coupling noise can bereduced.

Cell plate electrode lines CP0-CP2 are interconnection lines which arewide in the column direction, and the bit line cross sections can bemade, with sufficient margin, in the areas on the cell plate electrodelines.

Cell plate electrode lines CP may have a division configuration toconstitute a 2-port twin cell unit. In the case of the 2-port twin cellunit configuration, different row addresses may be substantiallysimultaneously accessed and sensing operation is performed. In such acase, capacitive coupling noises are reduced by the twisted bit lineconfiguration so that sensing operation can stably be performed.

FIG. 34 is a diagram showing an electrically equivalent circuit of thememory array according to the seventh embodiment of the presentinvention. FIG. 34 shows the twisted bit line configuration in which abit line of a bit line pair is arranged between the bit line of anotherbit line pair. A unit memory cell in the twin cell unit may be a 2-portmemory cell, or may be of the memory cell configuration in the thirdembodiment. FIG. 34 shows, as an example, the twisted bit lineconfiguration for a 2-port twin cell unit PTMU.

In FIG. 34, bit lines BLa and /BLa and bit lines BLb and /BLb areprovided to 2-port twin cell unit PTMU. Bit lines BLa and /BLa areconnected to a sense amplifier SAa for a port A, and bit lines BLb and/BLb are connected to a sense amplifier SAb for a port B. On a cellplate electrode interconnecting area CPA, bit lines BLa and /BLa have acrossing section. On a cell plate electrode interconnection area CPB,bit lines BLb and /BLb have a crossing section. Furthermore, on a cellplate electrode interconnecting area CPC, bit lines BLa and /BLa have acrossing section.

In bit lines BLa and /BLa for port A and bit lines BLb and/BLb for portB, the crossing sections are alternately disposed. Therefore, in thecase that a capacitive coupling noise is generated between bit lines BLaand /BLa and bit lines BLb and /BLb, in bit lines BLb and /BLb or bitlines BLa and /BLa the noises of the common phase are superimposed onthe two bit lines. Thus, the noises can be cancelled out upon sensingoperation. Therefore, even if in the 2-port memory, the two ports accessdifferent row addresses simultaneously and sense amplifiers SAa and SAbperform sense operation at substantially the same timing, the sensingoperation can be performed stably.

As described above, according to the seventh embodiment of the presentinvention, the bit lines have the crossing section on the cell plateelectrode. As a result, it is unnecessary to provided the areasexclusively for providing the crossing sections. Moreover, a bit lineconfiguration which is highly resistant against bit line noises can beachieved without any area penalty.

Eighth Embodiment

FIG. 35 is a diagram schematically showing a cross sectional structureof a memory cell according to an eighth embodiment of the presentinvention. FIG. 35 shows the cross sectional structure of DRAM cellsconstituting a twin cell unit. In FIG. 35, the DRAM cell includesimpurity regions 111 and 112 formed apart from each other on a surfaceof a P type semiconductor substrate region 110, a conductive line 113formed, on a not shown insulated gate insulating film, on the surface ofthe substrate area between impurity regions 111 and 112, and aconductive line 115 formed, in the same layer as conductive line 113, ona not shown capacitor insulating film formed on the surface of substratearea 110 adjacent to impurity region 112. The portion facing toconductive line 115 on the surface of semiconductor substrate region 110is an inversion layer forming region 116, and may be an impurity regionhaving the same conduction type as impurity regions 111 and 112 buthaving a low impurity concentration. The inversion layer forming regionmay be the impurity region having the impurity concentration adjusted,or may be merely a region having the impurity concentration of thesurface of the semiconductor substrate area 110 adjusted.

Conductive layer 113 constitutes a word line WL and conductive line 115constitutes a cell plate electrode CP of a memory cell capacitor. Anarray power supply voltage VCCS is applied to conductive line 115.Impurity region 111 is connected to a bit line BL. A memory celltransistor composed of conductive line 113 and impurity regions 111 and112 is made of a logic transistor having a low threshold voltage. In thesame way, conductive line 115 constitutes a cell plate transistor havinga low threshold voltage in a surface region of substrate area 110,wherein the concentration of the impurity is adjusted. Array powersupply voltage VCCS is applied to cell plate electrode CP.

Therefore, both of the memory transistor and cell plate transistor areformed through the same process for manufacturing the logic transistorthat has a low threshold voltage and is a component of the logic.

FIG. 36 is a diagram representing signal waveforms upon reading out dataof the memory cell shown in FIG. 35. It is assumed that a single wordline WL0 is selected or two word lines WL0 and WL2 are simultaneouslyselected to read out complementary data on bit lines BL and /BL, asshown in FIG. 36. The selected word line(s) WL is/are driven up to arraypower supply voltage level VCCS. When an L level data is written, bitline BL is driven into a ground voltage level. The memory celltransistor enters a sufficiently deep ON state. A channel is formedbetween impurity regions 111 and 112. The L level data is transmitted toimpurity region 112. When impurity region 112 receives the L level data,inversion layer 116 is formed in an inversion layer forming region(diffusion layer) in the substrate surface just under conductive line(cell plate electrode) 115 when the L level data is transmitted to adiffusion region (impurity region for adjusting the threshold voltage)in a cell plate transistor (that is, a transistor composed of conductivelayer 115 and the capacitor insulating film and substrate surface areaunder the capacitor insulating film). This is because array power supplyvoltage VCCS is applied to conductive line 115. As a result, the L leveldata is stored in inversion layer 116.

On the other hand, upon writing an H level data, a signal at array powersupply voltage level VSCC is transmitted to impurity region 111 throughbit line BL. The selected word line(s) WL is/are driven into array powersupply voltage level VCCS. In the memory cell transistor, the voltagelevel of impurity region 111 attains the voltage level equal to that ofthe gate electrode of the memory cell transistor. Thus, the inversionlayer is not sufficiently formed in the channel region. Therefore, thevoltage level of voltage VCCS-Vth at most is transmitted to impurityregion 112, where Vth is the threshold voltage of the memory celltransistor.

In the cell plate transistor, a depletion layer is expanded fromimpurity region 112 to the region just under electrode interconnectionline 115 by the H level data (voltage VCCS-Vth) of impurity region 112.Thus, inversion layer 116 is not sufficiently formed in the inversionlayer forming region (a MOS capacitor is not formed.) Thus, inversionlayer 116 is insufficiently formed, and therefore, electric charges arenot sufficiently supplied in the diffusion region 116 for forminginversion (inversion forming region). As a result, the H level datacannot be stored and held by this cell plate transistor (MOS capacitor).

When the H level data is written, charges corresponding to the H leveldata are accumulated in a junction capacitance Cj between impurityregion 112 and semiconductor substrate region 110.

Now, it is supposed that data in this memory cell (DRAM cell) are readout as shown in FIG. 36. Selected word line (sub word line) WL0 only isdriven or word lines (sub word lines) WL0 and WL2 are simultaneouslydriven into a select state. The precharge voltage of bit line BL is atarray power supply voltage level VCCS. When selected word line(s) WL(WL0 and/or WL2) is/are driven to array power supply voltage level VCCS,impurity region 112 serves as a source in the memory cell (DRAM cell)storing the L level data. Therefore, the memory cell transistor turnssufficiently into an ON state. Since inversion layer 116 is sufficientlyformed, charges accumulated in the memory cell capacitor and junctioncapacitance Cj are read out onto the corresponding bit line BL. Thus,the voltage of this bit line significantly drops. FIG. 36 shows thesignal waveform in the case that the L level data is read out ontocomplementary bit line /BL.

On the other hand, in the memory cell (DRAM cell) storing the H leveldata, the precharge voltage level of bit line BL is array power supplyvoltage level VCCS and is equal to the gate electrode voltage thereof.The voltage level of the impurity region 112 is also H level.Furthermore, no cell plate transistor (MOS capacitor) is formed(Inversion layer 116 is not sufficiently formed). Therefore, only thevoltage of the junction capacitance Cj of impurity region 112 can beseen from the side of bit line BL. Even if the voltage of the storagenode of the memory cell storing the H level data drops during the dataholding period, the amount of outflow electric charges is sufficientlysmall if the capacitance of junction capacitance Cj is sufficientlysmall. Even if the voltage level of the storage node of the memory cellstoring the H level data drops during holding data, the ratio ofjunction capacitance Cj to bit line capacitance is small when data areread out on the bit line, and a drop in the voltage of the bit line canbe made sufficiently small.

As shown in FIG. 36, therefore, a voltage difference between the H leveldata and the L level data can be made sufficiently large so that datacan be read out in the twin cell mode. Thus, a semiconductor memorydevice superior in data retention characteristics can be achieved.

In order to make the capacitance value of junction capacitance Cjsufficiently small, in the step of implanting impurities intosources/drains in the manufacturing process, a mask or the like is usedto perform only low-concentration N (N-type) ion-implantation, in whichthe implantation amount of the impurity is small, to impurity region 112in the memory array area. In this way, the capacitance value of junctioncapacitance Cj between impurity region 112 and substrate region 110 canbe made sufficiently small.

In this case, ion implantation is performed in the surface of substrateregion 110 facing to cell plate electrode conductive line 115, so as toproduce a low-concentration P type (P-type) impurity region in the sameway as in logic transistors. Thus, the threshold voltage of the cellplate transistor (MOS capacitor) can be made small. The impurityconcentration in this inversion layer forming region is madesubstantially equal to that of the impurity concentration in the channelregion of the memory transistor. As a result, both of the memory celltransistor and the cell plate transistor are made into a MOS transistorhaving a low threshold voltage substantially equal to that of the logictransistors. The memory transistor and the cell plate transistor aremanufactured by the same process for manufacturing the logic transistorsexcept the ion implantation in impurity region 112 in the storage node.By the same process for manufacturing the logic transistors, transistorsof peripheral circuitry are also manufactured. Therefore, the impurityconcentration in impurity region 112 is made lower than that in theperipheral transistors of the peripheral circuitry.

According to the eighth embodiment, the voltage level of the selectedword line (sub word line) is array power supply voltage VCCS, and aboosted word line boosting scheme for turning the memory celltransistors sufficiently into an ON state is not used. Therefore,similarly to the capacitor insulating film under cell plate electrodeline 115, the gate insulating film under the memory cell transistor canbe formed with the insulating film of a CMOS logic transistor having athin gate insulating film. Thus, the memory cell array can be formed bythe same manufacturing process for manufacturing the merged logic.

In the eighth embodiment of the present invention, a word line voltagenon-boosting scheme is used so that no circuit for boosting a selectedword lines is necessary. Thus, current consumption can be reduced.

Ninth Embodiment

FIG. 37 is a diagram schematically showing a layout of an array sectionof a semiconductor memory device according to a ninth embodiment of thepresent invention. In the layout shown in FIG. 37, active areas AR arearranged in alignment in the column direction. In each active area AR,two memory cells adjacent in the column direction are formed.

Bit lines BL0, /BL0, BL1 and /BL1 are arranged corresponding to theareas AR arranged in alignment in the column direction. Each of bitlines BL0, /BL0, BL1 and /BL1 is connected to active area AR arranged inthe corresponding column through a bit line contact BCT.

Two sub word lines SWL are arranged sandwiching bit line contacts BCTarranged in alignment in the row direction. In FIG. 37, sub word linesSW1 and SW2 are arranged sandwiching bit line contacts BCT in alignmentin the row direction. Sub word lines SW3 and SW4 are arrangedsandwiching bit line contacts BCT in alignment in the row direction.Therefore, two sub word lines SWL are arranged between the bit linecontacts for the active areas AR adjacent in the column direction.

Cell plate electrode lines CP1, CP2, CP3 and CP4 are arranged extendingin the row direction, corresponding to the respective sub word linesSWL1, SWL2, SWL3 and SWL4. The cell plate electrodes adjacent in thecolumn direction are isolated from each other. Cell plate electrodes CP0and CP5 are arranged corresponding to not shown sub word lines.

The voltages of cell plate electrodes CP0-CP5 are individuallycontrolled, as will be described later in detail. Even if the voltagelevel of the cell plate electrode CP arranged to a selected memory cellis changed so that bit line read out voltages are different between an Llevel data and an H level data in a non-boosted word line scheme, asufficient voltage difference between the bit lines is ensured.

A twin cell unit TMU is composed of two memory cells MC1 and MC2adjacent in the row direction to store a 1-bit data. In the case of thelayout shown in FIG. 37, bit lines and BL and /BL are alternatelyarranged corresponding to the columns of active areas AR. One bit lineis arranged at the pitch of the memory cells, and bit line contact BCTcan be formed just under bit lines BL and /BL. The shown layout is“closest packing cell arrangement” similarly to the layout illustratedin FIG. 24. Therefore, the memory cells can be arranged in high density.By arranging bit lines BL and /BL adjacently to each other, a folded bitline configuration can be achieved.

In the ninth embodiment, cell plate electrodes CP are divided andarranged, corresponding to respective sub word lines SWL. Cell plateelectrodes CP0-CP5 and sub word lines SWL1-SWL4 are made of theinterconnection lines of the same interconnecting layer, and made of asilicon-containing material, for example, polysilicon having an impuritydoped (doped polysilicon), polysilicide such as WSix and CoSix, orsalicide. The interconnection lines formed in the same layer as cellplate electrodes CP0-CP5 and sub word lines SWL1-SWL4 are also used asgate electrode interconnection lines for the transistors in a CMOS logicprocess for forming the logic integrated with the semiconductor memorydevice on the same semiconductor chip. Therefore, sub word lines SW andcell plate electrodes CP are formed by the same manufacturing processfor manufacturing gate electrodes of transistors of the logic integratedon the same semiconductor chip.

FIG. 38 is a diagram schematically showing a cross sectionalconfiguration taken along line 37A-37B in FIG. 37. In FIG. 38, memorycells are formed in the surface of a semiconductor substrate region 120.A memory transistor MT includes impurity regions (diffusion layers) 121and 122 formed apart from each other in the surface of semiconductorsubstrate region 120, and a gate electrode layer 124 formed, with a gateinsulating film 130 laid under, on the surface of substrate area 120between diffusion layers 121 and 122. Gate electrode layer 124constitutes a sub word line SWL.

A memory capacitor MQ includes a storage node electrode layer 123 formedon the surface of semiconductor substrate region 120, and a conductivelayer 125 arranged facing to storage node electrode layer 123 with acapacitor insulating film 131 interposed. A storage node electrode layer123 a of an adjacent memory cell and storage electrode layer 123 areinsolated from each other by a cell isolation region 126. Cell isolationregion 126 may have a trench type isolation configuration.Alternatively, a cell isolation oxide film may be formed, and thesurface thereof is made flat by CMP process or the like. A conductivelayer 125 and a conductive layer 125 a for the cell plate electrode CPof an adjacent memory cell are isolated from each other.

The conductivity type of impurity regions 121 and 122 and theconductivity type of semiconductor substrate region 120 areappropriately determined dependently on whether memory cell transistorMT is formed of an N channel transistor or a P channel transistor. FIG.38 shows, by way of example, the structure in which the memory cell isformed of an N channel MOS transistor and the conductivity type ofimpurity regions 121 and 122 is an N type.

Impurity region 121 is connected to a conductive layer 127 which isformed of, for example, a first level metal interconnection layer andconstitutes a bit line, through bit line contact BCT.

First level metal interconnection line 127 constituting the bit line isformed above conductive layers 124 and 125 constituting sub word lineSWL and cell plate electrode CP. Accordingly, in this memory cell array,the so-called CUB configuration is achieved. Memory cell capacitor MQ iscomprised of storage node electrode layer 123 formed in the surface ofsemiconductor substrate area 120 and conductive layer 125 arrangedfacing to this storage node electrode layer 123, and has a planarcapacitor configuration. Storage node electrode layer 123 may beconstructed by an impurity diffusion layer formed in the surface ofsemiconductor substrate region 120, or may be merely constructed ofsubstrate region 120 (the inversion layer in the surface of thesubstrate area serves as a capacitor electrode).

When a sub word line SWL is selected, a channel is formed betweenimpurity regions 121 and 122. Storage node electrode layer 123 connectedto impurity region 122 is electrically connected to bit line BL(conductive layer 125) through bit line contact BCT.

If the dual gate oxide film process is used to make the gate insulatingfilm 130 just under sub word lines SWL different in thickness fromcapacitor insulating film 131 just under cell plate electrodes CP, it isnecessary to use a mask to apply selective etching process. Thus, it isnecessary to consider mask tolerance. In addition, a resist film has tobe correctly exposed by an exposing ray while preventing diffusedreflection upon patterning of the film. Therefore, the interval betweenconductive layer 124 constituting sub word lines SWL and conductivelayer 125 constituting cell plate electrodes CP has to be made large.Therefore, in the case that the dual gate oxide film process is used formaking gate insulating film 130 different in thickness from capacitorinsulating film 131, the memory cell size increases. For this reason,gate insulating film 130 formed just under sub word lines SWL is madethe same in thickness as capacitor insulating film 131 just under cellplate electrode layer CP, and the two insulating films are made by thesame manufacturing process.

By using isolating region 126 having the surface height is made equal tothat of semiconductor substrate region 120 to isolate the memory cells,it is possible to reduce portions projected from the surface ofsemiconductor substrate region 120 upwardly, to lower the height ofconductive layers 125 and 125 a constituting cell plate electrode layerCP, for making a step relative to the peripheral circuitry sectionsmall.

As shown in FIG. 38, therefore, it is unnecessary to add a newinterconnection layer for cell plate electrode layer CP and the storagenode. Since the planar capacitor configuration is used for memory cellcapacitors to construct cell plate electrodes CP and sub word lines(word lines) SWL with interconnection lines on the same interconnectionlayer, any step between the memory array section and the peripheralcircuitry section is not produced. Thus, it is unnecessary to introduceflattening (planarization) processes, such as CMP, for relaxing the stepdue to the capacitor electrode. The memory cell array can be formedthrough CMOS logic process.

Each cell plate electrode CP is arranged in pairs with sub word lineSWL, and the voltages of the cell plate electrodes are changed in a unitof memory cell row.

For example, when a row active command is applied to select a row ofmemory cells and then a sub word line is selected, the capacitors of thetwo memory cells are simultaneously connected to the bit lines arrangedin a pair. For example, when sub word line SWL1 is selected in FIG. 37,the storage nodes of memory cells MC1 and MC2 are connected to bit linesBL0 and /BL0, respectively, so that memory data in memory cells MC1 andMC2 are read out onto the corresponding bit lines BL0 and /BL0. Memorycells MC1 and MC2 constitute twin cell unit TMU. The H level data isstored in one of the cells, and the L level data is stored in the other.

Sense amplifier connected to the pair of bit lines BL and /BLdifferentially amplifies a voltage difference ΔVb1 between thecorresponding bit lines BL0 and /BL0 or BL1 and /BL1. The voltagedifference ΔVb1 is represented by the following expression:ΔVb1=Cs·(V(SN,H)−V(SN,L))/(Cs+Cb),where Cs represents the capacitance of memory cell capacitor MQ, Cbrepresents the parasitic capacitance of each of bit lines BL and /BL,V(SN, H) represents the voltage of the storage node storing the H leveldata, and V(SN, L) represents the voltage of the storage node storingthe L level data,

By the sense operation of this sense amplifier, the bit line connectedto the memory cell storing the H level data is driven to array powersupply voltage level VCCS and the bit line connected to the memory cellstoring the L level data is driven to the ground voltage level (0 V).

As shown in FIG. 38, the planar capacitor is a MOS capacitor having agate electrode thereof serving as cell plate electrode CP. By forming aninversion layer in the surface of this semiconductor substrate region(Si: silicon), a desired capacitance can be ensured. Capacitorinsulating film 131 is a thin insulating film which is identical to gateinsulating film 130 of the memory cell transistor. From the viewpoint ofthe reliability of capacitor insulating film 131, it is desired that avoltage VCP applied to cell plate electrode CP does not exceed the arraypower supply voltage VCCS. Here, the memory transistor is formed of alogic transistor manufactured through the same process for manufacturingthe transistors of the logic and a non-boosted word line scheme isemployed. The voltage of the sub word line is at the level of the arraypower supply voltage when selected.

In order to form an inversion layer easily in storage node electrodelayer 123, it can be considered that “capacitor dope” process may beadopted, in which an N type impurity and a P type impurity arecounter-doped to the inversion forming region for an NMOS type memorycell and for a PMOS type memory cell, respectively. The NMOS type memorycell is a memory cell having an access transistor formed of an N channelMOS transistor, and its semiconductor substrate region is a P typesemiconductor substrate region. As for the PMOS type memory cell, theconductivity types thereof are reversed with respect to PMOS memorycell.

When a MOS capacitor is used in the logic integrated with thesemiconductor memory device on the same semiconductor chip, the impurityregions are interconnected to a predetermined voltage source (the powersupply voltage or the ground level) dependently on the voltage level ofthe gate electrode. The gate to source voltage of MOS capacitor in thelogic is a logic power supply voltage level in absolute value, and aninversion layer can easily be formed. Therefore, standard CMOS logicprocess for forming such logic does not particularly include the step ofperforming “capacitor dope” process for forming the inversion layer.Consequently, if such “capacitor dope” process is applied to memory cellcapacitors in the manufacturing process for forming the logic andsemiconductor memory cells on the same semiconductor chip, it isnecessary to additionally perform the “capacitor dope” process which isnot included in the CMOS logic process for forming the logic. Thus, aproblem that the cost for wafer process increases arises.

When such “capacitor dope” process is performed, it is required, for thefollowing reasons, to make the distance between conductive layer 124constituting the sub word line and conductive layer 125 constituting thecell plate electrode longer than a predetermined value.

FIG. 39 is a diagram schematically showing the impurity implantingregion in the capacitor dope process. In FIG. 39, the same referencenumerals are attached to the components corresponding to those of thememory cells shown in FIG. 38, and detail description thereof isomitted.

In the case of an NMOS type memory cell MT, the channel dope process foradjusting the threshold voltage of the access transistor of the memorycell is performed on the entire surface of the memory cell array.

However, it is necessary to perform the capacitor dope process not onthe channel region of the memory cell transistor but on the storage noderegion thereof. There is a restriction that it is necessary to preventany effect on the characteristics of NMOS memory cell transistor MT. Itis therefore necessary that the distance P between conductive layer 124constituting sub word line WL and conductive layer 125 constituting cellplate electrode CP is kept a predetermined value or more. In ionimplantation onto this storage node region, the following has to beprevented: the implanted impurity diffuses through a channel region 133in the lateral direction in heat treatment or annealing process, to varythe impurity concentration profile in the channel region 133 to lead tothe variation of the characteristics of access transistor MT.

As shown in FIG. 39, if the capacitor dope process is performed underthe sate that the distance between conductive layer 124 constituting subword line SWL and conductive layer 125 constituting cell plate electrodeCP is made smaller than the predetermined value P, there exists theregion 138 where the capacitor dope is not performed in the storage noderegion, because the impurity implantation is performed while thisdistance P is kept. Therefore, this storage node region includes theregion where an inversion layer is formed by counter-doping (capacitordope region) 135 and the region 138 where no counter-doping is performedso that an inversion layer is not easily formed. Thus, such a problemarises that the capacitance of the MOS capacitor cannot be sufficientlymade high.

Even if capacitor dope region 135 is not formed, the voltage of a nodeN1 (impurity region 123) is the ground voltage (0 V) with respect to thememory cell where an L level data is written in the twin cell mode ofstoring 1-bit data by two memory cells. The gate to source voltage ofthe MOS capacitor constituting this memory cell capacitor is at a levelof a cell plate voltage VCP (array power supply voltage level). As aresult, an inversion layer is formed in the semiconductor substrateregion and a capacitor having a desired capacitance is ensured for thememory cell capacitor.

On the other hand, in the memory cell where an H level data is written,the voltage level of node N1 is at a level of VCCS-ΔV, where ΔVindicates the voltage drop due to the threshold voltage loss of theaccess transistor by non-boosting of sub word line SWL.

In this case, the gate to source voltage of the MOS capacitorconstituting the memory cell capacitor assumes VCP−(VCCS−ΔV). Thus, instorage node region 123, an inversion layer cannot be sufficientlyformed and therefore, a desired capacitance of the memory cell capacitorcannot be ensured. Accordingly, in the case that the H level data isstored, a sufficient amount of charges cannot be accumulated in thestorage node. As shown in FIG. 40, a read out voltage ΔVH on the bitline when the H level data is read out is smaller than a read outvoltage ΔVL when the L level data is read out. Read out voltages ΔVH andΔVL when the H level data and the L level data are read out arerepresented by the following expressions, respectively:ΔVH=Csh·(V(SN,H)−(VCCS)/2)/(Csh+Cb),  (1)ΔVL=Csl·(VCCS/2−V(SN,L))/(Csl+Cb),  (2)where Csh and Csl represent the capacitance values of the memory cellcapacitor in reading out the H level data and the L level data,respectively. The precharge voltage of the bit lines is ½ of array powersupply voltage VCCS.

At the time of reading out memory cell data, therefore, the effectivereadout voltage ΔVH+ΔVL for the sense amplifier becomes smaller than theread out voltage difference expected in the twin cell mode. In the ninthembodiment, as a configuration for ensuring a sufficient read outvoltage difference in the non-boosted sub word line scheme, the cellplate voltage is changed for each selected row to change the voltagelevel of the storage node. Now, the configuration for controlling thecell plate voltage according to the ninth embodiment will be describedin the following.

FIG. 41 is a waveform diagram representing the operation in controllingthe cell plate voltage in the ninth embodiment of the present invention.Sub word line SWL0 is selected. The voltage of the selected sub wordline SWL0 is driven to a voltage level VWL. Data in the memory cellconnected to sub word line SWL0 are read out onto bit lines BL and /BL,and then sensing operation is performed. When the data are writtensubsequently, the voltage level of storage node N1 of this memory cellchanges dependently on the written data. Storage node N1 storing the Hlevel data attains a voltage level SN(H) while storage node N1 of thememory cell storing the L level data attains a voltage level SN(L).

After the completion of this writing of the data, or after thecompletion of data-readout in the operation of reading out the data, thevoltage level of cell plate electrode CP0, which is paired with selectedsub word line SWL0, is raised from the prescribed voltage VCP to apredetermined voltage level Va. In the state that the voltage of cellplate electrode CP0 is raised, the corresponding memory cell isconnected to the sense amplifier through the bit line and the voltagelevel of storage node N1 does not change.

When sub word line SWL0 is driven into a non-select state, for example,at the ground level after the access cycle is completed, the voltage ofcell plate electrode CP0 is recovered to voltage level VCP, which is theoriginal prescribed voltage. In the memory cell, sub word line SWL0attains the ground voltage level and the access transistor thereof is ina non-conductive state. Therefore, storage node N1 is in an electricallyfloating state. In response to the voltage drop of cell plate electrodeCP0, the voltage level of storage node N1 drops through capacitancecoupling. In FIG. 41, the voltage level of storage node N1 storing the Hlevel data drops by ΔVSNH, and the voltage level of storage node N1storing the L level data drops by ΔVSN.

When sub word line SWL0 is selected, read out voltages ΔVHA and ΔVLAappearing on bit lines BL and /BL are represented by the followingexpressions:ΔVHA=ΔVH−Csh·ΔVSNH/(Csh+Cb), andΔVLA=ΔVL−Csl·ΔVSNL/(Csl+Cb),where ΔVH and ΔVL are the read out voltages represented by theabove-mentioned expressions (1) and (2), respectively.

Consequently, the effective read out voltage ΔVHA+ΔVLA for the senseamplifier changes by the amount represented by the following expression:Csl·ΔVSNL/(Csl+Cb)−Csl·ΔVSNH/(Csh+Cb).

Because of Csl>>Csh, the second term of this read out voltage differencecan be neglected. Thus, a read out voltage ΔV can be substantiallyrepresented by the following expression:ΔV=ΔVH+ΔVL+Csl·ΔVSNL/(Csl+Cb).

Therefore, the read out voltage can be increased substantially byCsl·ΔVSNL/(Csl+Cb).

Therefore, even when a non-doped planar capacitor is used as the memorycell capacitor, reduction in effective utilization efficiency of thismemory cell capacitor can be prevented so that a sufficiently large readout voltage difference can be ensured.

In the operation waveform shown in FIG. 41, data writing operation to aselected memory cell is shown. However, this is also true for the memorycell from which data are read out. Storage node N1 of the memory cellconstituting a twin cell unit is set to voltage SN(H) or SN(L),dependently on the storage data.

FIG. 42 is a diagram schematically showing the configuration of asection for driving the cell plate electrodes and the sub word lines. InFIG. 42, a sub word driver SWD is provided to sub word line SWL, and acell plate electrode driver CPD is provided to cell plate electrode CP.Sub word driver SWD drives sub word line SWL into a select state inaccordance with sub decode signals SD and ZSD and a signal on acorresponding main word line ZMWL. On the other hand, cell plateelectrode driver CPD changes the voltage level of cell plate electrodeCP in accordance with a signal on the corresponding main cell plate lineZMCP and sub decode signals SD and ZSD. The amplitudes of sub decodesignals SD and ZSD are at the level of the peripheral power supplyvoltage or the array power supply voltage and is not boosted to highvoltage VPP level. In other words, as the manner for driving sub wordline SWL, a non-boosted word line driving scheme is used.

Single main word line ZMWL is provided for sub word lines of pluralrows, and single main cell plate line ZMCP is provided for cell plateelectrodes CP of plural rows. Main word line ZMWL and main cell plateline ZMCP are arranged corresponding to each other, for example, in thesame interconnection layer. On the other hand, sub word lines SWL areformed in the same interconnection layer as cell plate electrodes CP.

When main word line ZMWL is driven into a select state and sub word lineSWL is driven into a select state in accordance with sub decode signalsSD and ZSD, main cell plate line ZMCP is driven into a select state withdelay of a certain time so that cell plate electrode driver CPD changesthe voltage level of the corresponding cell plate electrode CP. Whenmain word line ZMWL is driven into a non-selected state, main cell plateline ZMCP is also driven into a non-selected state so that cell plateelectrode driver CPD transmits the prescribed voltage VCP to thecorresponding cell plate electrode CP. After selected sub word line SWLis driven into the non-selected state, the voltage level of cell plateelectrode CP returns to the original voltage level. Consequently, thevoltage of storage node N1 drops through capacitance coupling.

In the case that the memory cell transistor is formed of a P channel MOStransistor, the semiconductor substrate region is an N type substrateregion. Thus, the direction along which cell plate voltage VCP is drivenis reversed with respect to that for the N channel MOS memory celltransistor.

FIG. 43 is a diagram showing an example of the configuration of cellplate driver CPD shown in FIG. 42. In FIG. 43, cell plate electrodedriver CPD includes a P channel MOS transistor TQ1 for transmitting, tocell plate electrode CP, a sub decode signal SD* obtained bylevel-converting sub decode signal SD into the voltage level Va inaccordance with a signal on main cell plate line ZMCP, an N channel MOStransistor TQ2 for transmitting, to cell plate electrode CP, cell platevoltage VCP on a cell plate voltage transmitting line 150 in response toa signal voltage on main cell plate line ZMCP, and an N channel MOStransistor TQ3 for connecting cell plate voltage transmitting line 150to cell plate electrode CP in accordance with complementary sub decodesignal ZSD.

Cell plate voltage VCP of a predetermined voltage level generated fromVCP generating circuit shown in FIG. 1 is transmitted to cell platevoltage transmitting line 150.

When the corresponding sub word line is driven into a selected state,sub decode signal SD is at H level and complementary sub decode signalZSD is at L level. When main cell plate line ZMCP is driven into L levelof a selected state in this state, P channel MOS transistor TQ1 turns onso that level converted sub decode signal SD* is transmitted to cellplate electrode CP. At this time, MOS transistors TQ2 and TQ3 are innonconductive states and cell plate electrode CP provided to the memorycells in the selected row is isolated from cell plate voltagetransmitting line 150. In the configuration in which cell plate voltagetransmitting line 150 transmits cell plate voltage VCP in common to thememory cells connected to the non-selected sub word lines in the memoryarray as well, a voltage at the peripheral power supply voltage levelcan be transmitted to cell plate electrode CP without causing anyadverse effect on cell plate voltage VCP.

When main cell plate line ZMCP attains H level, MOS transistor TQ1 turnsinto a nonconductive state and MOS transistor TQ2 turns into aconductive state. Thus, cell plate voltage VCP on cell plate voltagetransmitting line 150 is transmitted to cell plate electrode CP.

When main cell plate line ZMCP is in the non-selected state of H leveland the level converted sub decode signal SD* is at L level,complementary sub decode signal ZSD is at H level so that cell platevoltage transmitting line 150 is connected to cell plate electrode CP.Accordingly, cell plate voltage VCP is reliably transmitted from cellplate voltage transmitting line 150 to the cell plate electrodes CPprovided for the memory cells in the non-selected rows.

In the configuration of cell plate electrode driver CPD shown in FIG.43, cell plate voltage VCP is assumed to be at the voltage level of ahalf of array power supply voltage level VCCS. Therefore, even ifcomplementary sub decode signal ZSD is at H level of the peripheralpower supply voltage level, cell plate voltage VCP can reliably betransmitted to cell plate electrode CP.

Even if cell plate voltage VCP is array power supply voltage level VCCS,array power supply voltage VCCS can reliably transmitted to cell plateelectrode CP with the following conditions: sub decode signals SD andZSD are signals each having the amplitude of peripheral power supplyvoltage VCCP, and a voltage difference between array power supplyvoltage VCCS and peripheral power supply voltage VDDP is greater thanthe absolute values of the threshold voltages of MOS transistors TQ2 andTQ3.

In the block division configuration of the memory array, sub decodesignals SD* and ZSD are driven by a sub decode driver arranged at thecrossing section (cross band) between the sense amplifier band where thesense amplifiers are arranged and the sub word driver band where the subword drivers are arranged. It is therefore necessary that levelconverted sub decode signal SD* drives both of the sub word line and thecell plate electrode, and it is necessary to make the driving power ofthe sub word driver large. However, by making large the drivingcapability of the sub decode driver arranged at the cross band andhaving a level conversion function, the voltage level of cell plateelectrode CP arranged corresponding to a selected row can also bechanged dependently on the selected sub word line. Particularly, becauseno memory cell is connected to cell plate electrode CP, the capacitancethereof can be made small and a large driving power is not required forthe sub decode driver.

If the non-boosted word line scheme is employed, the sub decode signalat the array power supply voltage or the peripheral power supply voltageis transmitted. In this configuration, a level converter for levelconverting the sub decode signal SD is provided for driving the cellplate electrode, and the sub decoder for generating the sub decodesignal is not required to drive the sub word line and the cell plateelectrode. Such level converter can be arranged at the cross band.

For a main cell plate line driver for driving main cell plate line ZMCP,the same configuration as that of the main word driver for driving mainword line ZMWL can be used. Only by making different the driving timingof the main cell plate line driver from the activating timing of themain word driver for driving the main word line, main cell plate lineZMCP can be driven into a selected state in the same manner as main wordline ZMWL. By using the delay signal of a main word driver activatingsignal as an activating signal for the main cell plate line driver, themain cell plate line can easily be driven into a select state at adesired timing.

FIG. 44 is a diagram showing another configuration of the main cellplate line driver. In FIG. 44, main word line ZMWL is driven by a mainword driver 152. On the other hand, main cell plate ZMCP is driven by afall delay circuit 154 that receives output signals of main word driver152.

Main word driver 152 drives a corresponding main word line ZMWL into thelevel of the ground voltage when the corresponding main word line ZMWLis in a selected state. Therefore, by using fall delay circuit 154, maincell plate line ZMCP is driven into a selected state after apredetermined time passes from the time when main word line ZMWL isdriven into a selected state. Although it is necessary to increase theoutput driving power of main word driver 152, it is unnecessary toprovide a decoding circuit for selecting main cell plate line ZMCPseparately from a main row decoder for decoding the main word lineaddress. Thus, circuit occupancy area can be reduced.

The voltage level of cell plate electrode CP is changed after the accesstransistor of the memory cell turns into a nonconductive state. Thevoltage level of the storage node is then changed through capacitancecoupling. Consequently, sub decode signals SD* and ZSD to main cellplate line ZMCP and the cell plate electrode are driven into anon-selected state at a slightly later timing than signals for the subword lines. This can easily realized by using appropriateinterconnection delay or gate delay.

FIG. 45 is a diagram showing a further configuration of the main cellplate line selecting circuit. In the configuration shown in FIG. 45,main cell word line ZMWL is driven by main word driver 152, and maincell plate line ZMCP is driven by main cell plate driver 156. Main worddriver 152 drives the corresponding main word line ZMWL into a selectedstate in response to the activation of a main word line driving timingsignal RXT while a main cell plate driver 156 drives the correspondingmain cell plate line ZMCP into a selected state in accordance with acell plate line driving timing signal RXTD.

A main row decoding circuit 158 is provided in common to main worddriver 152 and main cell plate driver 156. A main word line designatingsignal from main row decoding circuit 158 is applied in common to mainword driver 152 and main cell plate driver 156.

The activating timing of main cell plate driving timing signal RXTD ismade later than that of main word line driving timing signal RXT. Inthis way, main cell plate line ZMCP can be driven into a selected stateonly in a predetermined time period at a precise timing. Since main worddriver 152 is required only to drive main word line ZMWL, main word lineZMWL can be driven into a selected state at a high speed.

FIG. 46 is a diagram schematically showing an example of the arrangementof the sub word lines and the cell plate electrodes. In FIG. 46, mainword line ZMWL and main cell plate line ZMCP are arranged extending inthe row direction. Sub word lines SWL0-SWL3 are arranged correspondingto main word line ZMWL, and cell plate electrodes CP0-CP3 are arrangedcorresponding to main cell plate line ZMCP. Sub word drivers SWD0-SWD3are arranged corresponding to sub word lines SWL0-SWL3, and cell plateelectrode drivers are arranged corresponding to cell plate electrodesCP0-CP3. Adjacently to the cell plate electrode and the sub word linearranged in a pair, corresponding drivers SWD and CPD are arranged.

In a not shown sense amplifier band, sub decode drivers SDRE and SDROare arranged corresponding to sub word driver bands. Sub decode driverSDRE generates sub decode signals SD*0, SD*2, ZSD0 and ZSD2, and subdecode driver SDRO generates sub decode signals SD*1, SD*3, ZSD1, andZSD3.

In the arrangement shown in FIG. 46, therefore, it is merely requiredthat cell plate driver CPD is arranged at the crossing section of thesub word driver band and the sense amplifier band. Thus, cell plateelectrode driver CPD can easily be arranged without changing the layout.

Cell plate voltage transmitting line 150 for transmitting cell platevoltage VCP may be arranged in the same interconnecting layer as mainword line ZMWL and main cell plate line ZMCP. In the arrangement of thiscell plate voltage transmitting line, it is merely required that thearray power supply voltage line for transmitting power supply voltage tothe sense amplifiers in the sense amplifier does not butt with theinterconnection line for the cell plate voltage.

In the arrangement shown in FIG. 46, the sub decode drivers SDRE andSDRO generate the level converted sub decode signals SD*. However, thenon-boosted word line scheme is employed, the sub decode drivers SDREand SDRO are required to generate the non-boosted sub decode signal SDand the level converted sub decode signal SD* for the sub word line andfor the cell plate line, respectively.

[Modification 1]

FIG. 47 is a diagram showing the configuration of a modification 1 ofthe cell plate electrode driver. In FIG. 47, cell plate electrode driverCPD includes an N channel transistor TQ4 rendered conductive, when asignal on main cell plate line ZMCP is at H level, for connecting cellplate electrode line CP electrically to cell plate voltage transmittingline 150, a capacitance element 160 connected to cell plate electrodeCP, a P channel transistor TQ5 rendered conductive, when a signal onmain cell plate line ZMCP is at L level, for transmitting a levelconverted sub decode signal SD* to capacitance element 160 when madeconducive, and an N channel MOS transistor TQ6 rendered conductive, whencomplementary sub decode signal ZSD is at H level, for connecting cellplate electrode CP to cell plate voltage transmitting line 150.

Cell plate electrode CP is arranged corresponding to the memory cells inone row in a corresponding memory block. However, cell plate electrodeCP is an electrode layer facing to the storage node of the memory cellcapacitor, and has no gate capacitance connected thereto, but only aninterconnection parasitic capacitance is present thereon. Therefore, bysetting the capacitance of capacitance element 160 to an appropriatevalue, the voltage level of cell plate electrode line CP can be raisedby charge pumping operation of capacitance element 160 when levelconverted sub decode signal SD* attains H level.

In other words, in the configuration of cell plate electrode driver CPDshown in FIG. 47, when a signal on main cell plate line ZMCP is at Hlevel, MOS transistor TQ4 is rendered conductive and cell plate voltagetransmitting line 150 is electrically connected to cell plate electrodeCP so that cell plate electrode CP is kept at the predetermined level ofcell plate voltage VCP. At this state, MOS transistor TQ5 is in anonconductive state, and level converted sub decode signal SD* causes noeffect on cell plate voltage CP.

On the other hand, when the signal on main cell plate line ZMCP turns Llevel, MOS transistor TQ5 enters a conductive state and MOS transistorTQ4 enters a nonconductive state. When sub decode signal SD turns Hlevel in this state, complementary sub decode signal ZSD is at L leveland MOS transistor TQ6 enters a nonconductive state. The voltage levelof cell plate electrode CP rises up through the charge pumping operationof capacitance element 160. When sub decode signal SD* turns L level,cell plate electrode CP returns to the original voltage level throughthe charge pumping operation of capacitance element 160. If the timingof the deactivation of level converted sub decode signal SD* is set suchthat the deactivation is subsequent to the deactivation of the main wordline, the voltage level of the storage node can be lowered after thememory transistor in a selected memory cell turns nonconductive. In thiscase, however, it is required that main cell plate line ZMCP is in aselected state. It is sufficient for achieving such control of thedeactivation that main cell plate ZMCP is driven into a non-selectedstate at a timing later than main word line ZMWL is driven into anon-selected state.

On the other hand, when a signal on main cell plate line ZMCP is at Llevel and sub decode signal SD is at L level, complementary sub decodesignal ZSD is at H level and MOS transistor TQ6 turns conductive.Therefore, even if MOS transistor TQ5 is in a nonconductive state inthis state, cell plate electrode CP is electrically connected to cellplate voltage transmitting line 150 and the cell plate electrode CP iskept at cell plate voltage level VCP.

In the case that the configuration shown in FIG. 47 is used, the voltageof cell plate electrode CP can be raised to a desired level dependentlyon the relationship between the capacitance value of capacitance element160 and the interconnection capacitance of cell plate electrode CP.Although the level converted sub decode signal SD* is used, sub decodesignal SD before the level conversion may be used. The voltage level ofthe sub decode signal should be set dependently on the capacitance ofcell plate electrode CP and the capacitance of capacitance element 160.

In the above-mentioned configuration shown in FIG. 47, the cell plateelectrode is arranged corresponding to the sub word line. Each of cellplate electrode driver CPD changes the voltage of the cell plateelectrode. for each memory cells on a selected row. The voltages of thestorage nodes of the necessary minimum memory cells are changed so thatcurrent consumption can be reduced. Because the selected memory cellsstore valid data and therefore, the voltages of the storage nodes ofonly the selected memory cells are changed. Non-accessed memory cells donot store valid data. Even if the voltages level of the data in thesenon-accessed memory cells are changed, the stored data are invalid data.Thus, only useless power is consumed. In order to reduce such powerconsumption, the cell plate voltage is changed for each memory cells ona selected row.

However, in the case of a block division configuration in which thememory array is divided into plural blocks and driving into aselected/non-selected state is performed in a unit of a memory block,the cell plate electrode may be changed in a unit of a memory block. Inthis case, power consumption increases. However, the access transistorsof the memory cells connected to a non-selected row are in anonconductive state. Therefore, even if cell plate voltage VCP changesso that the voltage level of the corresponding storage node SN (node N1)rises, the voltage of the storage node returns to the original voltagelevel when the voltage of the cell plate electrode returns again to theoriginal voltage level. As a result, the amount of charges accumulatedin the storage node of a non-selected memory cell does not change.

Therefore, even if the cell plate electrode is driven for each memoryblock, no problems are caused except for issues associated with powerconsumption and response speed. In the case that the cell plateelectrode is driven in a unit of a memory block, it is merely requiredthat the cell plate electrode driver is arranged for each memory block.The cell plate voltage can be controlled in accordance with a blockselecting signal for specifying a memory block. Thus, the circuitconfiguration for controlling the cell plate voltages is made simple andcircuit occupancy area can be reduced.

As described above, according to the ninth embodiment, the cell platevoltages of the memory cells are changed. Therefore, even with anon-boosted sub word line scheme, a sufficient read out voltagedifference can be produced between the corresponding bit lines even ifthe capacitance of the capacitor in the memory cell having a planarcapacitor configuration is effectively reduced.

Tenth Embodiment

FIG. 48 is a diagram schematically showing the configuration of an arraysection of a semiconductor memory device according to a tenth embodimentof the present invention. In FIG. 48, active areas AR for forming 2-bitmemory cells that are adjacent and in alignment in the column directionare arranged in alignment in the column direction. Each of bit lines BLand /BL is arranged corresponding to each column of active areas AR.Each of bit lines BL and /BL is electrically connected to the activeareas in the corresponding column through bit line contacts BCT. Theactive areas adjacent in the column direction are isolated from eachother by a cell isolation region.

Two word lines are arranged in a pair to sandwich bit line contacts BCTarranged in alignment in the row direction. In FIG. 48, word line WL0and WL1 are arranged sandwiching bit line contacts BCT aligned in therow direction, and word lines WL2 and WL3 are arranged sandwiching bitline contacts BCT aligned in the row direction and extending in the rowdirection. Word lines WL (WL0-WL3) are formed of interconnection linesof a first level polysilicon interconnection layer.

Cell plate electrodes CP are formed of interconnection lines of a secondlevel polysilicon interconnection layer. Cell plate electrodes CPconstitute one-side electrodes of planar capacitors of memory cellcapacitors, which will be described later.

Cell plate electrodes CP are formed into a division configuration inwhich they are separated from each other in the column direction in thememory cell array. However, cell plate electrodes CP are formed ofinterconnection lines of the interconnection layer different from theinterconnection layer for word lines WL (WL0-WL3) and therefore, eachcell plate electrode CP is formed overlapping partially with acorresponding word line WL. By forming cell plate electrodes CP so as tooverlap partially with the corresponding word lines WL, the areas ofstorage node regions facing to cell plate electrodes CP can be made aslarge as possible. Moreover, the interval between each cell plateelectrode CP and the corresponding sub word line SWL (word line WL) canbe made short. It is also unnecessary to consider boundaries of the subword lines at upon patterning of the cell plate electrodes, to make thepatterning easy.

A twin cell unit is composed of memory cells MC1 and MC2 adjacent in therow direction, and a 1-bit data is stored by these two memory cells MC1and MC2.

FIG. 49 is a diagram schematically showing a cross sectional structuretaken along line 48A-48A in FIG. 48. In FIG. 49, a memory cell MCincludes impurity regions 171 and 172 formed apart from each other inthe surface of a semiconductor substrate area 170, a conductive layer173 formed, with a gate insulating film 174 laid thereunder, on thechannel region between impurity regions 171 and 172, and a conductivelayer 175 formed, with a capacitor insulating film 176 laid thereunder,on impurity region 172.

Conductive layer 173 is composed of an interconnection line of the firstlevel polysilicon interconnection layer, and constitutes word line WL.On the other hand, conductive layer 175 is composed of aninterconnection line of the second level polysilicon interconnectionlayer, and constitutes cell plate electrode CP. These conductive layers173 and 175 are formed in different production process steps. Therefore,cell plate electrode CP can be formed extending onto word line WL.

Impurity region 171 is connected to a conductive layer 177 of a firstlevel metal interconnection layer through bit line contact BCT.Conductive layer 177 constitutes bit line BL (or /BL). Impurity region172 is isolated from other memory cells by a cell isolation region 178.

In the configuration of memory cell MC shown in FIG. 49, a memory celltransistor MT is composed of impurity region 171, conductive layer 173,and gate insulating film 174. A memory cell capacitor MQ is formed ofcapacitor insulating film 176 between impurity region 172 and conductivelayer 175.

When memory cell MC shown in FIG. 49 is formed, the first levelpolysilicon interconnection layer provides conductive layer 173 to be aword line WL. Next, impurities are, in self-alignment with the wordline, implanted, to form impurity regions 171 and 172, which in turnconstitute the source/drain region and the storage node region of thememory cell transistor. In the case that the access transistor of thememory cell is an N channel MOS transistor, impurity regions 171 and 172are N type impurity regions. The memory cell transistor may be formed ofa P channel MOS transistor.

After impurity regions 171 and 172 are formed, the second levelpolysilicon interconnection layer is patterned to form cell plateelectrode CP. In the case of the configuration as shown in FIG. 49,therefore, word line WL and cell plate electrode CP are formed ofinterconnection lines of the different interconnection layers, and areformed in different manufacturing process steps. As a result, theinterval between word line WL and cell plate electrode CP can be madesufficiently small. Impurity region 122 shown in FIG. 38 can be removed,and the size of the memory can be reduced. Just under cell plateelectrode CP, impurity region 172 is formed. Thus, regardless of thelogic level of memory data, the utilization efficiency of memory cellcapacitor MQ can be made 100%, and the capacitance thereof can bedecided dependently on the facing area of conductive layer 175constituting cell plate electrode CP and impurity region 172.

Conductive layer 173 constituting the gate electrode of memory celltransistor MT is formed through dual polysilicon gate process for thefirst level polysilicon interconnection layer in CMOS logic process. Inthe case that the transistor gate is formed by this dual polysilicongate process, for an N channel MOS transistor, an N type impurity isimplanted into its channel region. At this time, impurity ions areimplanted into the channel region through the gate electrode of thetransistor and therefore, the gate electrode of the memory celltransistor is formed of an N type polysilicon interconnection line. Onthe other hand, for a P channel MOS transistor, a P type impurity isimplanted into its channel region through the gate electrode in order tomake the absolute value of its threshold voltage small and therefore,the gate electrode of the memory cell transistor is formed of a P typepolysilicon interconnection line.

In the case that cell plate electrode CP is made of the polysilicon ofthe same interconnection layer constituting transistor gate electrodeserving as (sub) word line WL, cell plate electrode CP is also formed ofthe impurity-implanted polysilicon interconnection line. In this case,however, it can be considered that by a depletion layer (gate depleting)generated in the polysilicon, a cell plate voltage VCP applied to cellplate electrode CP is divided by the capacitance of the depletion layerso that the effective film thickness of the capacitor insulating filmbecomes thick and thus the effective capacitance thereof is reduced.

As shown in FIG. 49, however, conductive layer 175 constituting cellplate electrode CP is formed by a process different from a process forforming conductive layer 173 constituting word line WL. Accordingly,conductive layer 175 constituting cell plate electrode CP can be formedof doped polysilicon doped with a high-concentration N type impurity orP type impurity, independently of conductive layer 173 constituting wordline WL. As a result, no gate depleting is caused in the dopedpolysilicon, into which the high-concentration impurity is implanted andthus, a reduction in the effective capacitance of memory cell capacitorMQ can be prevented so that a desired capacitance of the memory cellcapacitor can be ensured.

Capacitor insulating film 176 formed just under cell plate electrode CPis manufactured by a process different from a process for manufacturinggate insulating film 174 just under word line WL and therefore,capacitor insulating film 176 can be made of a highly dielectric filmsuch as Ta2O3 film. By using such a highly dielectric film as capacitorinsulating film 176, the area of memory cell capacitor MQ can be reducedso that the size of the memory cell can be made very small.

In the case of using this highly dielectric film, a highly dielectricfilm is also formed in the region where conductive layer 173constituting word line WL and conductive layer 175 constituting cellplate electrode CP overlap with each other. As a result, a capacitanceis present between word line WL and cell plate electrode CP. It can betherefore considered that the parasitic capacitance of word line WLwould become large so that word line WL could not be driven into aselect state at a high speed. Thus, in the region where word line WL andcell plate electrode CP overlap with each other, the thickness of theinterlayer dielectric film is made as large as possible. In this way,the parasitic capacitance of word line WL is reduced.

In the case that this highly dielectric film is used as capacitorinsulating film 176, a capacitor can be composed of conductive layer 173constituting word line WL and conductive layer 175 constituting cellplate electrode CP. Accordingly, the manufacturing step of a poly topoly capacitor, which is used in an analogue circuit included in thesystem LSI, can be used as the manufacturing step of forming conductivelayer 173, capacitor insulating film 176 and conductive layer 175. Inthis case, the thickness of the insulating film between word line WL andcell plate electrode CP is made as large as possible to reduce theparasitic capacitance of word line WL. Preferably, dual capacitorinsulating film process is used to make the thickness of capacitorinsulating film 176 in the region where cell plate electrode CP andimpurity region 172 are facing to each other different from thethickness of the interlayer dielectric film in the region where wordline WL and cell plate electrode CP overlap with each other.

Word line WL is discussed in the foregoing description. However, wordline WL may be a word line of a non-hierarchical configuration, or maybe a sub word line SWL in the hierarchical word line configuration.

[Modification 1]

FIG. 50 is a diagram schematically showing a layout of a modification 1of the tenth embodiment of the present invention. In FIG. 50, activeareas AR are arranged in the column direction such that active areas ARin the adjacent rows are shifted by ½ pitch of memory cells in the rowdirection. Bit lines are arranged corresponding to active areas AR inalignment in the column direction. In FIG. 50, bit lines BL0, /BL0, BL1and /BL1 are representatively shown.

Word lines WL1-WL3 are arranged extending in the row direction, and areformed of, for example, the first level polysilicon interconnectionlayer. Cell plate electrodes CP are arranged in parallel to word linesW11-WL3. A part of each of cell plate electrodes CP is located so as tooverlap with the corresponding word line WL. Cell plate electrodes CPare formed of, for example, the second level polysilicon interconnectionlayer. A cell plate electrode CP is provided in common to memory cellsarranged in two rows. Cell plate electrodes CP adjacent in the columndirection are separated from each other.

In the layout shown in FIG. 50, two bit lines are arranged in the pitchof the memory cells in the row direction. Bit lines contacts BCT arearranged corresponding to alternate bit lines in the row direction.

Upon selecting a memory cell, the word lines arranged oppositely to eachother with respect to cell plate electrode CP are simultaneously driveninto select states. For example, word lines WL1 and WL2 aresimultaneously driven into the select state. In this case, memory cellMC1 is connected to bit line BL0 through bit line contact BCT, andmemory data in memory cell MC2 are read out onto bit line /BL0. In thesame way, memory cell data are simultaneously read out onto bit linesBL1 and /BL1. A twin cell unit is therefore composed of two memory cellsMC1 and Mc2 arranged in the different rows.

In this layout of the memory cells, by using interconnection linesformed by different manufacturing processes for cell plate electrodes CPand word lines WL, the size of the memory cells can be significantlyreduced. Since the impurity region is used as the storage node, memorycell capacitors can be regularly formed regardless of a logic level ofstorage therein. Thus, the utilization efficiency of the capacitors canbe improved so that memory cell capacitors having a small occupancy areaand a desired capacitance can be achieved.

[Modification 2]

FIG. 51 is a diagram schematically showing the configuration of a memorycell section of a modification 2 of the tenth embodiment of the presentinvention. In the layout shown in FIG. 51, rectangular active areas ARfor forming 2-bit memory cells are arranged in alignment in the columndirection. Bit lines BL and /BL are alternately arranged correspondingto the columns of active areas AR. Each of active areas AR is connectedto the corresponding bit line BL or /BL through bit line contact BCT.

A pair of two word lines is arranged sandwiching bit line contact BCTand extending in the row direction.

Cell plate electrodes CP0-CP3 are arranged corresponding to word linesWL0-WL3, respectively. The voltage level of each of cell plateelectrodes CP0-CP3 can be set independently on each other (see the ninthembodiment). Cell plate electrodes CP0-CP3 and word lines WL0-WL3 areformed by different manufacturing processes. Word lines WL0-WL3 areformed of the first level polysilicon interconnection layer, and cellplate electrode lines CP0-CP3 are formed of the second level polysiliconinterconnection layer. Cell plate electrodes CP0-CP3 are arrangedoverlapping partially with the corresponding word lines WL0-WL3,respectively.

In the configuration shown in FIG. 51 as well, the size of the memorycells can be reduced in the same way. Even if a boosted voltage higherthan the array power supply voltage is not transmitted to a selectedword line WL, a sufficiently large readout voltage difference can begenerated between bit lines BL and /BL. Since the electrodes of memorycell capacitor MQ are composed of the cell plate electrode and theimpurity region formed in the surface of the semiconductor substrateregion, the memory cell capacitor can reliably be formed regardless ofthe logic level of storage data. Thus, charges corresponding to thestorage data can be accumulated correctly.

As described above, according to the tenth embodiment of the presentinvention, word lines and cell plate electrodes are formed ofinterconnection lines of different interconnection layers and thedistance between the word line and the cell plate electrode can be madeshort so that the size of the memory cells can be reduced. Moreover, theimpurity region can be formed in the substrate surface and facing to thecell plate electrode, and the cell plate electrode can be formed ofdoped polysilicon so that the utilization efficiency of the capacitorcan be improved.

By forming the impurity region, as the storage node, in the surface ofthe substrate region, the memory cell capacitor can be formed regardlessof storage data and the utilization efficiency of the capacitor isimproved. Thus, electric charges can reliably be accumulated inaccordance with the storage data.

Eleventh Embodiment

FIG. 52 is a diagram schematically showing the configuration of an arraysection of a semiconductor memory device according to an eleventhembodiment of the present invention. FIG. 52 schematically shows thelayout of memory cells arranged in 2 rows and 2 columns. In theconfiguration in FIG. 52, word lines WL0-WL3 and cell plate electrodesCP are composed of different interconnecting layers. Cell plateelectrodes CP are interconnected to each other through a second levelpolysilicon interconnection line CPL. Therefore, the cell plateelectrodes are arranged in a meshed shape to be extended over a regionof the memory cell array except regions where bit line contacts BCT areformed.

The remaining configuration is the same as that shown in FIG. 48. Twomemory cells MC1 and MC2 adjacent in the row direction constitute a twincell unit. By selecting one word line WL, data of two memory cells areread out onto bit lines BL and /BL in a pair.

As shown in FIG. 52, by interconnecting cell plate electrodes CParranged extending over the region except the regions where bit linecontacts BCT are formed, the cell plate electrodes are arranged in ameshed shape inside the predetermined region. Therefore, only bysupplying a cell plate voltage VCP to several portions of the cell plateelectrodes, cell plate voltage VCP can stably be supplied to the cellplate electrodes of the memory cells in the predetermined region. Inaddition, it is not required to supply cell plate voltage VCP to thecell plate electrode CP in correspondence with each row. The occupancyarea of the circuit for supplying cell plate voltage VCP can be reduced.

FIG. 53 is a diagram showing the manner of distribution of cell platevoltage VCP. In FIG. 53, cell plate electrodes CP are interconnectedtogether so that cell plate electrode layer CPLY substantially having ameshed shape is formed. In cell plate electrode layer CPLY, holes areformed in the regions corresponding to bit line contacts BCT. Forexample, a cell plate voltage transmitting line 180 for transmittingcell plate voltage VCP is arranged in a sub word driver band, and cellplate electrode layer CPLY is connected to cell plate voltagetransmitting line 180 through cell plate voltage distributing lines 181.

In the same way, a cell plate voltage transmitting line 183 is arrangedin a sense amplifier band, and cell plate electrode layer CPLY isconnected to cell plate voltage transmitting line 183 through cell platevoltage distributing lines 184. Cell plate voltage transmitting lines181 and 183 for transmitting cell plate voltage VCP are composed of, forexample, a metal second interconnecting layer. From the second levelmetal interconnecting layer, cell plate voltage VCP is transmittedthrough cell plate voltage distributing lines 181 and 184 and cell plateelectrode layer CPLY formed of the second level polysiliconinterconnection layer. Therefore, it is unnecessary to supply cell platevoltage VCP to each of the cell plate electrodes (layers) formed into apiled or shunt configuration. Thus, only by arranging several cell platevoltage distributing lines in the sense amplifier band and/or the subword driver band, the occupancy area of the circuit for supplying cellplate voltage VCP can be reduced.

In the configuration in FIG. 53, cell plate electrode layer CPLY isarranged in common to the memory cells of memory sub arrays divided bythe sub word driver bands. Cell plate electrode layer CPLY can bearranged without causing any adverse effect on the layout of the subword drivers in the sub word driver bands.

Additionally, cell plate electrode layer CPLY can be arranged withoutcausing adverse effect on the sense amplifier circuits and bit lineperipheral circuits arranged in the sense amplifier bands.

Cell plate electrode layer CPLY may be arranged, in common to the memorysub arrays in a memory block, so as to extend in the row direction inthe same way as the main word lines. In the case that the cell platevoltage transmitting lines are formed in an interconnection layer belowthe main word line, holes are formed in the cell plate voltagetransmitting lines to shun the contacts for the main word lines and thesub word lines in a region where the contacts are formed. Since thecontact for a main word line and a sub word line is formed in a sub worddriver band, the cell plate electrodes are interconnected to each otherand cell plate connecting lines CPL are arranged shunning the sub worddrivers in the sub word driver band.

Cell plate electrode layers CPLY may be interconnected bridging over asense amplifier band. In the region where neither sense amplifiercircuit nor bit line peripheral circuit are present, the cell plateelectrode layers adjacent in the column direction are interconnectedtogether through the second level polysilicon interconnecting layer.

Therefore, cell plate electrode layer CPLY is merely required to beformed into a meshed shape. In the memory sub array, a hole is formed ata region of bit line contact BCT in cell plate electrode layer CPLY.Cell plate electrode layers CPLY may be interconnected together throughthe second level polysilicon interconnection layer without causingadverse influence on the layout of the sense amplifiers, the bit lineperipheral circuits and the sub word drivers.

As described above, according to the eleventh embodiment of the presentinvention, the cell plate electrode is formed into a meshed shape andcell plate voltage VCP is not required to be supplied for each cellplate electrode arranged corresponding to each respective memory cellrow. Thus, the area of the circuit layout for transmitting cell platevoltage VCP can be reduced.

Twelfth Embodiment

FIG. 54 is a diagram schematically showing the configuration of a memoryarray of a semiconductor memory device according to a twelfth embodimentof the present invention. In FIG. 54, each word line is composed of alow-resistance conductive layer made of, for example, a second levelmetal interconnection layer, and a word line made of a first levelpolysilicon interconnection layer. In this word line configuration,low-resistance metal word line WLM in an upper layer and polysiliconword line WL of a relatively high resistance in a lower layer areelectrically connected to each other through a contact SHT in a wordline shunt region. FIG. 54 shows word lines WL0-WL3 formed of the firstpolysilicon (1-poy), and metal word lines WLM0-WLM3 formed of, forexample, the second level metal interconnection layer arranged inparallel to word lines WL0-WL3.

In the word line shunt region, each metal word line WLM is electricallyconnected to the corresponding word line WL through contact SHT. Byarranging the low resistive metal word line in parallel to the word lineof a relatively high resistance polysilicon, transmitting a word lineselecting signal onto metal word line WLM, and connecting metal wordline WLM electrically to polysilicon word line WL at predeterminedpositions, the resistance value of polysilicon word line WL iseffectively made small and the word line is driven into a select stateat a high speed.

Such a configuration, in which polysilicon word line WL and metalinterconnection line WLM are interconnected together at predeterminedintervals, is called word line shunt configuration.

In such a word line shunt configuration, a cell plate electrodes CP arearranged in a meshed shape in the same way as in the eleventhembodiment. Contact SHT for word line shunt is extended from the secondlevel metal interconnection layer to the first level polysiliconinterconnection layer. In this region of the shunt contacts, a hole HOLis made in cell plate electrode CP. Cell plate electrode CP formed ofthe second level polysilicon interconnection layer can be arrangedextending over a predetermined region of the memory cell array withoutcausing an adverse effect on the word line shunt configuration. In thiscase, a hole is also made to cell plate electrode CP in the bit linecontact region, although not shown clearly in the FIG. 54.

Accordingly, holes are made in the word line shunt portions and the bitline contact portions to the cell plate electrode, and the cell plateelectrode is arranged continuously extending in the remaining region andhas a meshed configuration. In a non-hierarchical word lineconfiguration, therefore, the cell plate voltage is not required to besupplied for each memory cell row by forming the cell plate electrodesinto a meshed shape. Thus, the layout area for supplying the cell platevoltage can be reduced.

As described above, according to the twelfth embodiment, the hole ismade in the word line shunt region to cell plate electrode CP and cellplate electrode CP formed of the second level polysiliconinterconnection layer is arranged in a meshed shape on the memory cellarray without causing an adverse effect on the word line shuntconfiguration so that cell plate voltage VCP can stably be supplied.Moreover, the interconnection layout area for supplying the cell platevoltage can be reduced.

Thirteenth Embodiment

FIG. 55 is a diagram schematically showing a cross sectionalconfiguration of a memory cell according to a thirteenth embodiment ofthe present invention. In FIG. 55, the memory cell includes impurityregions 191 and 192 formed apart from each other in the surface of asemiconductor substrate area 190, a gate electrode 193 formed, with notshown gate insulating film laid thereunder, on the region betweenimpurity regions 191 and 192, and a capacitor electrode 194 formed, witha not shown capacitor insulating film laid thereunder, on a storage noderegion adjacent to an impurity region 194. This storage node region isisolated from other adjacent memory cells by a cell isolation region195.

A salicide 196 is formed on the surface of impurity region 191 andsalicide 196 is also formed on the surface of gate electrode 193.Moreover, a salicide 196 is formed on the surface of gate electrode 194.The salicide is a self-aligned polysilicide, and is a silicide layerformed of CoSi or the like and is formed in self-alignment in thesurface of polysilicon. The formation of the salicide reduces theresistance of polysilicon interconnection line and the impurity regionsas well.

Salicide 196 on impurity region 191 is electrically connected to bitline contact BCT, and this bit line contact BCT is connected to a bitline 198.

When the transistor of the memory cell is formed, impurity regions 191and 192 are formed in self-alignment. In general, a side wall insulatingfilm 197 is formed on the side of gate electrode 193. Side wallinsulating film 197 is formed of an insulating film of SiN, SiO, or thelike.

Side wall insulating film 197 is formed on the surface of impurityregion 192, and the surface of impurity region 192 is entirely coveredwith side wall insulating film 197. Gate electrode 193 and cell plateelectrode 194 are formed of polysilicon in the same interconnectionlayer. By setting the interval DW between gate electrode 193 and cellplate electrode 194 to a value two or less times larger than the widthof side wall insulating film 197 upon formation of the polysilicon, thesurface of impurity region 192 can be entirely covered with side wallinsulating film 197 upon formation of this side wall insulating film.

In order to lower gate electrode interconnection resistance anddiffusion layer (impurity layer) resistance, salicide process forforming silicide in self-alignment on the surface of silicon isintroduced in standard CMOS logic process. In the case that memory cellsare formed through CMOS logic process, salicide 196 is formed on thesurface of impurity region 191, gate electrode 193 and cell plateelectrode 194 as well. In the case that salicide 196 is formed on thesurface of impurity region 192, the resistance of impurity region 192 isreduced, but junction leakage current increases.

Impurity region 192 is adjacent to the storage node electrode andtherefore, in the case that the salicide is formed on the surface ofimpurity region 192, storage data may be lost out by the junctionleakage current. Thus, by covering the surface of impurity region 192with side wall insulating film 197, no salicide is formed on the surfaceof impurity region 192 even in the salicide process. Thus, it ispossible to suppress reduction in data retention characteristics.

It is suppressed that side wall insulating film 197 is formed beforethis salicide is formed or that salicide is formed on the sides of gateelectrode 193 and cell plate electrode 194. This side wall insulatingfilm is formed through anisotropic etching of an insulating film. In theanisotropic etching, the width of the side wall insulating film isdetermined. Accordingly, the width of the side wall insulating film canbe known in advance dependently on the anisotropic etching. Dependentlyon this width, the interval between the gate electrode and the cellplate electrode can be decided.

As described above, according to the thirteenth embodiment of thepresent invention, in the case that the cell plate electrode and thegate electrode are formed in the same manufacturing step, the intervalbetween gate electrode 193 and cell plate electrode 190 is set to avalue 2 or less times than the width of the side wall insulating film.Thus, even if the impurity region is formed in the surface of thesubstrate area between the gate electrode and the cell plate electrode,in subsequent formation of the side wall insulating film, the surface ofthe impurity region connected to the storage node can be covered withthe side wall insulating film. Therefore, it is possible to prevent theformation of salicide in this impurity region in salicide process, tosuppress junction leakage current. Consequently, electric chargesaccumulated in the storage node are prevented from being lost by leakagecurrent, and the deterioration of data retention characteristics can besuppressed.

In FIG. 55, the memory cell transistors may be formed of P channel MOStransistors or N channel MOS transistors. In either case, themanufacturing process for forming salicide is carried out.

Fourteenth Embodiment

FIG. 56 is a diagram schematically showing the configuration of a memoryarray section according to a fourteenth embodiment of the presentinvention. In FIG. 56, cell plate electrodes CP are arrangedcorresponding to sub word lines SWL. Each cell plate electrode CP isarranged corresponding to the sub word lines at both sides of the cellplate electrode. In other words, each cell plate electrode CP isarranged in common to memory cells in two rows. Specifically, in FIG.56, a cell plate electrode CP 12 is arranged corresponding to sub wordlines SWL1 and SW12, and a cell plate line CP03 is arrangedcorresponding to a sub word line SWL0 and a not shown sub word lineSWL3. A cell plate electrode CP 34 is arranged corresponding to a subword line SWL3 and a not shown sub word line SWL4.

Rectangular active areas AR are arranged in alignment in the columndirection. Bit lines BL and /BL are arranged corresponding to and inalignment with active areas AR, extending in the column direction. Eachactive area AR has 2-bit memory cells adjacent in the column directionformed therein and is electrically connected to the corresponding bitline BL or /BL through a bit line contact BCT. In the configurationshown in FIG. 56, a twin cell unit for storing 1-bit data is composed oftwo memory cells MC1 and MC2 adjacent in the row direction. In selectinga memory cell, one sub word line is driven into a select state. Bitlines BL and /BL are connected to a sense amplifier SA.

In the configuration shown in FIG. 56, cell plate electrodes CP and subword lines SWL are formed of interconnection lines of the sameinterconnection layer. The sub word lines and the cell plate electrodesare formed of a material containing silicon, such as polysilicon havingan impurity introduced therein (doped polysilicon), polysilicide such asWSix or CoSix, and salicide. Accordingly, cell plate electrodes CP andsub word lines SWL are formed in the same step for forming gateelectrodes of logic transistors. In the same way as in the ninthembodiment, the cell plate electrodes are arranged facing to inversionlayer forming regions in order to implement a planar capacitorconfiguration. No impurity regions are formed in the inversion layerforming regions. The voltage level of each cell plate electrode CP ischanged dependently on the selection/non-selection of the correspondingmemory cell.

FIG. 57 is a diagram showing operation waveforms of the fourteenthembodiment of the present invention in driving one cell plate electrode.Referring to FIGS. 56 and 57, description is made of the operation ofthe semiconductor memory device according to the fourteenth embodimentof the present invention.

Now, it is supposed that sub word line SWL 0 is selected. In this state,sub word line SWL0 is at a voltage level VWL and bit lines BL and /BLare at an array power supply voltage level VCCS and the ground level (0level), respectively, through sensing operation of sense amplifier SA.In this state, the voltage level of cell plate electrode CP03 arrangedcorresponding to sub word line SWL0 is driven into, for example, arraypower supply voltage level VCCS. On the other hand, the non-selectedcell plate electrodes are kept at the ground voltage level. Concerningthe voltage levels of storage nodes SN, dependently on storage data,storage nodes SN(H) storing an H level data and storage nodes SN(L)storing an L level data are at array power supply voltage level VCCS andat the ground level, respectively.

When one access cycle for writing and reading out data in memory cellsis completed, sub word line SWL0 in the select state is driven into anon-select state and the voltage level thereof is lowered to the groundvoltage level. Sense amplifier SA is deactivated so that bit lines BLand /BL are precharged and equalized to an intermediate voltage levelthrough a not shown precharging/equalizing circuit.

When sub word line SWL0 is driven into the non-select state and theaccess transistor of the memory cell turns nonconductive, cell plateelectrode CP03 is subsequently driven into the ground voltage level. Inthis way, the voltage level of storage node SN(H) storing the H leveldata lowers by a voltage ΔVSNH by capacitance coupling between this cellplate electrode and the corresponding storage node (inversion layer). Inthe same way, the voltage level of storage node SN(L) storing the Llevel data lowers by a voltage ΔVSNL. By setting the coupling efficiencyof the coupling capacitance to an appropriate value, voltage variationsΔVSNL and ΔVSNH of these storage nodes can be made smaller than avoltage variation of cell plate electrode CP03 (ΔVSNL<<VCCS).

In this state, cell plate electrode CP is at the ground voltage level,and storage node SN(L) storing the L level data is at a voltage level of−ΔVSNL. The gate to source voltage of the planar capacitor constitutingthis memory cell capacitor is ΔVSNL and is far smaller than array powersupply voltage VCCS. In this state, therefore, an inversion layer ismerely weakly formed in the semiconductor substrate region just underthe cell plate electrode in the case that the semiconductor substrateregion is of a P type substrate and is biased to a negative voltage VBBlevel. Since the impurity region constituting the storage node is keptat a negative voltage level, the potential of the impurity regionconstituting this storage node becomes higher than that of the inversionlayer. Thus, a potential barrier is formed between this inversion layerand the impurity region constituting the storage node.

Therefore, electrons hardly flow out from the impurity region of thestorage node into the substrate region just under the cell plateelectrode. Thus, it is possible to prevent electrons from flowing outfrom the impurity region of this storage node to the cell plateelectrode through the capacitor insulating film. As a result, thevoltage level of storage node SN(L) storing the L level data can be keptat a voltage level of about −ΔVSNL.

When sub word line SWL0 is again selected, the voltage level of cellplate electrode CP03 kept at the ground voltage level is first driveninto array power supply voltage VCCS and by capacitance coupling, thevoltage levels of storage nodes SN(H) and SN(L) are returned to theoriginal voltages VCCS and 0 volt level, respectively.

Subsequently, sub word line SWL0 is driven into a select state, andstorage nodes SN(H) and SN(L) are connected to the corresponding bitlines BL and /BL and then sensing operation is performed.

The read out voltages are ΔVH and ΔVL, and a read out voltage differenceis ΔVH+ΔVL. Thus, the read out voltage equivalent to that in the ninthembodiment can be realized in a non-boosted word line scheme. Therefore,in the case that a cell plate electrode is formed by CMOS logic processsimilarly to the gate electrode of a memory cell transistor, thethickness of a capacitor insulating film is thin similarly to the gateinsulating film, a cell plate electrode VCP cannot be easily boostedabove the array power supply voltage. According to the instant cellplate electrode control scheme, a sufficiently large read out voltagedifference can be generated in a pair of bit lines. It is also possibleto prevent electrons from flowing out to the cell plate electrodethrough the capacitor insulating film, and to prevent data retentioncharacteristics from deteriorating.

Each cell plate electrodes CP provided for the memory cells connected tothe other non-selected sub word pairs are kept at the ground voltagelevel. When one of the sub word lines in a pair is selected, the cellplate voltage of the memory cells connected to the non-selected sub wordline in this sub word line pair also changes. Since the memory celltransistor in this non-selected memory cell is in a nonconductive state,the storage node voltage thereof merely rises or falls throughcapacitance coupling. The voltage variations of the storage nodes arethe same between the rise and the fall in the capacitive coupling. Anaccess period is short in general. Even if electrons leak to the cellplate electrode through the capacitor insulating film during this accessperiod, the amount of the leakage charges is very slight. As a result,the leakage causes no adverse effect on storage data in the non-selectedmemory cells.

FIG. 58 is a diagram schematically showing a cross sectional structureof the memory cell according to the fourteenth embodiment of the presentinvention. In FIG. 58, a memory cell includes impurity regions 201 and202 formed apart from each other in the surface of a semiconductorsubstrate area 200, a gate electrode 203 formed, with a not shown gateinsulating film laid thereunder, on the region between impurity regions201 and 202, and a cell plate electrode 204 formed, with a not showncapacitor insulating film laid thereunder, on an inversion layer formingregion 206. Inversion layer forming region 206 is isolated from otherinversion layer forming regions by a cell isolation region 205.

Impurity region 201 is connected to a bit line 207 through a bit linecontact BCT.

In order to form an inversion layer sufficiently in inversion layerforming region 206, array power supply voltage VCCS is applied, as cellplate voltage VCP, through cell plate electrode 204. Even in anon-selected state (standby state) in this state, the inversion layer isformed in inversion layer forming region 206 when array power supplyvoltage VCCS is applied as cell plate voltage VCP. When impurity region202 is a storage node SN(L) storing an L level data, electronsaccumulated in impurity region 202 are transmitted to the inversionlayer formed in inversion layer forming region 206 so that the electronsflow into cell plate electrode line 204 through the capacitor insulatingfilm. In this case, therefore, accumulated charges (electrons) are lostin impurity region 202 so that the voltage level of storage node SN(L)storing the L level data rises as shown by a broken line in FIG. 57.

By keeping cell plate voltage VCP at the ground voltage level in thisnon-selected state (standby state), a change in cell plate voltage VCPcauses the voltage level of storage node SN(L) storing the L level datato be a negative voltage of −ΔVSNL on the basis of capacitance coupling.Although a voltage difference between the gate and source of the MOScapacitor is ΔVSNL in this case, the value of the voltage difference isby far smaller than array power supply voltage VCCS. Thus, no inversionlayer is substantially formed in the inversion formation region, but apotential barrier is formed in a boundary region 210 between impurityregion 202 and inversion layer forming region 206. In other words, thepotential of inversion layer forming region 206 becomes lower than thatof storage node SN(L) storing the L level data to prevent electrons fromflowing into inversion layer forming region 206 (Potential φ becomeshigher as the amount of accumulated electrons becomes larger).

Therefore, by driving the cell plate voltage VCP of this cell plateelectrode CP in the same way as the voltage level of the correspondingsub word line, the voltage level of storage node SN(L) storing the Llevel data can be kept at a negative voltage level in the standby state.Thus, it is possible to prevent electrons from flowing into cell plateelectrode 204.

Concerning the storage node storing the H level data, the voltage levelof the cell plate electrode is the ground voltage level and is lowerthan the voltage level of the storage node. Therefore, no inversionlayer is formed. In the same way, the PN junction between the impurityregion and the substrate-region is in a reverse-biased state so that noelectrons flow out.

When this memory cell is again selected, cell plate voltage VCP is againdriven into array power supply voltage VCCS so that an inversion layeris formed in inversion layer forming region 206. Furthermore, bycapacitance coupling, the voltage level of storage node SN(L) isreturned to the original voltage level (ground voltage level).

During this standby period, the voltage level of storage node SN(L) is anegative voltage level. Thus, it may be considered that leakage currentthrough the channel region just under word line WL increases, that is, aso-called disturb refresh immunity becomes weak. In this case,therefore, reduction in disturb refresh immunity can be prevented bysetting the voltage of the selected sub word line SWL into a negativevoltage level in the standby state.

FIG. 59 is a diagram schematically showing the configuration of asection for driving the cell plate electrode. In FIG. 59, a main wordline ZMWL is arranged corresponding to sub word lines SWL1-SWL4. Cellplate electrode CP12 is arranged between sub word lines SWL1 and SWL2.Cell plate electrode CP34 is arranged between sub word lines SWL3 andSW14.

Sub word drivers SWD1-SWD4 are arranged corresponding to sub word linesSWL1-SWL4, respectively. Sub word drivers SWD1 and SWD 2 are arranged inone of the sub word driver bands arranged at both sides in the rowdirection of this memory cell sub array. Sub word drivers SWD3 and SWD4are arranged at the other side of these sub word driver bands at theboth sides. Sub word drivers SWD1-SWD4 receive sub decode signalsSD1-SD4, respectively. When main word line ZMWL is in a selected stateand the corresponding sub decode signal SD is driven into H level orinto a selected state, the corresponding sub word line SWL is driveninto H level of a selected state. Complementary sub decode signalsZSD1-ZSD4, not shown in FIG. 59 for the simplicity of the figure, areapplied to sub word drivers SWD1-SWD4, respectively.

A cell plate driver CPD0 is arranged corresponding to cell plateelectrode CP12, and a cell plate driver CPD1 is arranged correspondingto cell plate electrode CP34. Cell plate driver CPD0 is arrangedadjacently to sub word drivers SDW1 and SWD2 and receives a signal onmain cell plate line ZMCP and sub decode signals SD1 and SD2. Cell platedriver CPD1 is arranged adjacently to sub word drivers SDW3 and SWD4 andreceives a signal on main cell plate line ZMCP and sub decode signalsSD3 and SD4.

When the signal on main cell plate line ZMCP is at L level and subdecode signals SD1 or SD2 is in a selected state, cell plate driver CPD0drives the corresponding cell plate electrode CP12 into a level of, forexample, array power supply voltage VCCS. When the signal on main cellplate line ZMCP is at L level and sub decode signal SD3 or SD4 is in aselected state, cell plate driver CPD1 drives the corresponding cellplate electrode CP34 into the level of array power supply voltage VCCS.

For the configuration of the section for driving main cell plate lineZMCP and main word line ZMWL, the configuration shown in FIG. 45 can beemployed.

In the configuration shown in FIG. 59, main cell plate line ZMCP isfirst driven into a select state, as represented by signal waveforms inFIG. 60. After main cell plate line ZMCP is driven into the selectedstate, the voltage level of the cell plate electrode corresponding tothe selected sub word line rises in accordance with sub decode signalsSD<4:1> generated concurrently. As a result, the voltage levels of thestorage nodes of the memory cells corresponding to an addressed row risethe capacitance coupling. Then, main word line ZMWL is driven into aselected state, and in accordance with sub decode signals SD<4:1>, a subword line SWL corresponding to a addressed row is driven into a selectedstate. At this time, the voltage levels of the storage nodes restore tothe ground voltage level and the array power supply voltage level,respectively. Read out voltages ΔVH and ΔVL are transmitted onto thecorresponding bit line pair.

After the access cycle is completed, main word line ZMWL is first driveninto a non-selected state and the sub word line is driven intonon-selected state. Then, main cell plate line ZMCP is driven into anon-selected state of H level. In response to the driving of main cellplate line ZMCP into the non-selected state, the output signal of thecell plate driver CPD in the selected state attains to L level of theground voltage level. The sub word line is in the non-selected state,and the access transistors of the selected memory cells are already innonconductive states, and therefore, the voltage levels of the storagenodes drop through capacitance coupling.

Consequently, by setting the active period of main cell plate line ZMCPlonger than that of main word line ZMWL, the voltage levels of thestorage nodes of the selected memory cells can be changed throughcapacitance coupling, when cell plate voltage VCP is changed while thememory cell transistors are kept in the nonconductive state.

Cell plate drivers CPD0 and CPD1 may be composed of an OR circuit thatreceives sub decode signals SD1 and SD2 or SD3 and SD4, and an ANDcircuit that receives an inversion signal of a signal on main cell plateline ZMCP and an output signal of this OR circuit.

[Modification]

FIG. 61 is a diagram schematically showing a modification of thefourteenth embodiment of the present invention. In the configurationshown in FIG. 61, main word line ZMWL is arranged corresponding to subword lines SWL1-SWL4, and main cell plate line ZMCP is provided for cellplate electrodes CP12 and CP 34. Complementary sub decode signals areapplied to sub word drivers SWD1-SDW4 arranged corresponding to sub wordlines SWL1-SWL4, respectively, in a conventional art. That is, subdecode signals SD1 and ZSD1 are applied to sub word driver SWD1, and subdecode signals SD2 and ZSD2 are applied to sub word driver SWD2. Subdecode signals SD3 and ZSD3 are applied to sub word driver SWD3, and subdecode signals SD4 and ZSD4 are applied to sub word driver SWD4.

A cell plate driver CPDb, which receives a signal on main cell plateline ZMCP and complementary sub decode signals ZSD3 and ZSD4, isprovided to cell plate electrode CP12. A cell plate driver CPDa, whichreceives a signal on main cell plate line ZMCP and complementary subdecode signals ZSD1 and ZSD2, is provided to cell plate electrode CP34.Sub word drivers SWD1 and SWD2 and cell plate driver CPDb are arrangedoppositely with respect to the memory sub array section, in sub worddriver bands. Sub word drivers SWD3 and SWD3 and cell plate driver CPDaare arranged oppositely with respect to the memory sub array section.

Each of cell plate drivers CPDb and CPDa is composed of a compositegate. Cell plate drivers CPDa and CPDb receive the corresponding subdecode signals ZSD1 and ZSD2 or ZSD3 and ZSD4, respectively, and furtherreceive a signal on main cell plate line ZMCP. The composite gateconstituting cell plate driver CPDb (CPDa) includes an AND gate whichreceives the corresponding complementary sub decode signals ZSD3 andZSD4 (ZSD1 and ZSD2), and a gate circuit which receives an output signalof this AND circuit and a signal on main cell plate line ZMCP. The gatecircuit outputs a signal of H level when the signal on main cell plateline ZMCP is at L level and the output signal of the AND circuit is at Hlevel, so as to drive the corresponding cell plate electrode CP12 orCP34 into the array power supply voltage level.

For example, when sub word line SWL3 or SWL4 is selected, both of subdecode signals ZSD1 and ZSD2 are at H level and sub decode signals SD1and SD2 are at L level. One of sub decode signals SD3 and SD4 is at Hlevel and the other is at L level. Therefore, when sub decode signalSWL3 or SWL4 is selected, the output signal of cell plate driver CPDb isat L level and the output signal of cell plate driver CPDa turns Hlevel.

When sub decode signal SWL1 or SWL2 is selected, one of complementarysub decode signals ZSD1 and ZSD2 turns L level and both of sub decodesignals ZSD3 and ZSD4 are at H level. In this case, therefore, theoutput signal of cell plate driver CPDb turns H level and the outputsignal of cell plate driver CPDa is kept at L level. As a result, evenif the configuration shown in FIG. 61 is used, the voltage level of thecell plate electrode arranged corresponding to a selected sub word linecan be kept at H level in an active cycle and can be kept at L level ina standby state.

Upon transition to the standby state, all of sub decode signalsZSD1-ZSD4 are at H level, but the signal on main cell plate line ZMCPturns H level and the output signals of cell plate drivers CPDb and CPDaturn L level.

According to the configuration as shown in FIG. 61, cell plate driversCPDa and CPDb and sub word drivers SWD1 to SWD4 can be alternatelyarranged at both sides of the memory sub array along the row direction.Thus, the layout can be made easy.

For the configuration of sub word drivers SWD1-SWD4, the configurationof sub word drivers in the prior art can be used.

In the case that the memory cell transistor is formed of a P channel MOStransistor, the driving direction of the cell plate voltage is reversedto the above operation. Specifically, the cell plate voltage is kept atthe array power supply voltage level in the standby, and the cell platevoltage is kept at the ground voltage level in the access cycle.

In the above-mentioned configuration, cell plate electrode CP isarranged corresponding to two sub word lines and in common thereto. Asshown in FIG. 46, however, cell plate electrodes CP1-CP4 may be arrangedcorresponding to sub word lines SWL1-SWL4, respectively. In this case,as cell plate drivers with the configuration equivalent to that of thesub word drivers, can be used. During the active cycle period, the cellplate electrode arranged corresponding to a selected sub word line canbe driven into the array power supply voltage or a predetermined voltagelevel merely by making the activating timing of main word line ZMWLdifferent from that of main cell plate line ZMCP.

For the configuration in which cell plate electrodes are arranged in ameshed shape, such a configuration may be employed that the cell plateelectrode layer is driven in a unit of memory blocks including thememory sub arrays aligned in the row direction and a cell plateelectrode interconnection line provided to a memory block including aselected word line is driven by a cell plate driver, for example, inaccordance with a memory block selecting signal. In this memory block, amain word line is arranged extending in the row direction, and a maincell plate line is also arranged extending in the row direction.

In the configuration of a hierarchical word line configuration, 4 subword lines are connected to one main word line. However, an 8-wayhierarchical word line configuration may be employed in which 8 sub wordlines are provided to one main word line.

A negative logic signal is transmitted on the main cell plate line.However, a positive logic signal may be transmitted on the main cellplate line for providing the timing for driving the cell plateelectrode.

As the word line configuration, a non-hierarchical word lineconfiguration may be used. In the case of this non-hierarchical wordline configuration, a cell plate driver having the same configuration asthe word driver is used to drive the corresponding cell plate electrode.However, in the case that the cell plate electrode is provided to twoword lines, the cell plate driver drives the corresponding cell plateelectrode into a selected state in accordance with the signals forselecting the corresponding two word lines. As the configuration forsuch arrangement, an OR circuit may be employed that receives word lineselecting signals for selecting the corresponding two word lines.

As described above, according to the fourteenth embodiment of thepresent invention, in a standby state, the voltage of the storage nodestoring an L level data is kept at a negative voltage level and uponstart of an active cycle, this storage node voltage is returned to theoriginal voltage level. A potential barrier is formed between thestorage node and the inversion layer forming region to prevent outflowof electrons. As a result, it is possible to prevent the voltage of thestorage node storing the L level data from rising. Thus, a sufficientlylarge read out voltage can be read out onto the corresponding bit line.Thus, data retention characteristics can be significantly improved inthe semiconductor memory device of a non-boosted word line scheme.

Fifteenth Embodiment

FIG. 62 is a diagram schematically showing a layout of a memory cellarray according to a fifteenth embodiment of the present invention. FIG.62 representatively shows the layout of memory cells arranged in 4 rowsand 2 columns. In the layout of the memory cells shown in FIG. 62, acell plate electrode CP is arranged commonly to memory cells MC arrangedin two rows in the same way as in the layout shown in FIG. 48.

Active areas AR are arranged in alignment in the column direction. Eachactive area AR has a 2-bit DRAM cells formed therein.

A bit line BL or /BL is arranged corresponding to active areas ARaligned in the column direction. Bit lines BL and /BL are electricallyconnected to the corresponding active areas through bit line contactsBCT. These bit line contacts BCT are arranged in alignment in the rowdirection.

Word lines WL are arranged to be opposite to each other with respect tobit line contacts BCT arranged in alignment in the row direction. Wordlines WL0 and WL1 are arranged oppositely to each other with respect tothe bit line contacts BCT. Word lines WL2 and WL 3 are arrangedoppositely to each other with respect to bit line contacts BCT.

In the layout shown in FIG. 62, memory cells MC1 and MC2 arrangedadjacently to each other in the row direction store 1-bit data. That is,complimentary data are stored in memory cells MC1 and MC2, and thestorage data in these memory cells MC1 and MC2 are read out onto bitlines BL and /BL simultaneously.

Each memory cell MC (active area AR) is isolated from the adjacentmemory cell (active area AR) by a buried insulating film formed in atrench region. Cell plate electrode CP constitutes a capacitor with adiffusion layer formed in a side wall of this isolating trench.Therefore, an effective capacitor region MQ is wider than active areaAR.

FIG. 63 is a diagram schematically showing a cross sectional structuretaken along line 62A-62A in FIG. 62. In FIG. 63, memory cell MC isformed on a P-type semiconductor substrate region 300. A memory celltransistor MT includes N-type impurity regions 302 and 303 formed apartfrom each other on the surface of this P-type semiconductor substratearea 300; and a conductive layer 305 formed, with a gate insulating filmlaid thereunder, on a region between impurity regions 302 and 303. Thisconductive layer 305 constitutes word line (sub word line) WL, and ismade of a silicon-containing material, such as polycrystal silicon intowhich an impurity is introduced (ion-implanted polysilicon or dopedpolysilicon), polycide such as WSix or CoSix, or salicide.

In effective capacitor region MQ, a side wall of a trench region 310 forisolating this memory cell is utilized to constitute a capacitor. Trenchregion 310 isolates adjacent memory cells (active areas) by means ofburied insulating film 312 formed in the bottom of the trench.

A conductive layer 306 constituting cell plate electrode CP is formedwith capacitor insulating films 308 (308 a and 308 b) laid thereunder onthis semiconductor substrate area 300 and the bottoms and the side wallsof trench regions 310. Conductive layer 306 is made of the same materialas conductive layer 305 constituting word line WL, and is formed in thesame interconnection layer. That is, cell plate electrodes CP and wordlines WL are formed in the same manufacturing process. A cell platevoltage VCP is applied to conductive layer 306.

Conductive layer 306 includes a conductive layer 306 a arranged facing,through capacitor insulating film 308 a, to a storage node (inversionlayer) 307 a formed on the surface of semiconductor substrate area 300;a conductive layer 306 b arranged facing, through a storage node(inversion layer) 307 b and capacitor insulating film 308 b, to the sidewall of trench region 310; and a conductive layer 306 c formed on buriedinsulating film 312 and at the bottom of the trench region. Theseconductive layers 306 a, 306 b and 306 c are continuously extended inthe row direction, and arranged commonly to the memory cells arranged inalignment in two rows.

The storage nodes of the memory cells adjacent to each other in the rowdirection and in the column direction are isolated from each other bythis buried insulating film 312. Storage node 307 is formed of aninversion layer. However, an impurity may be introduced into storagenode 307.

The area of the capacitor can be effectively made large by means ofconductive layer 306 b facing to storage node 307 b formed on the sidewall of trench region 310. By isolating the memory cells (active area)by means of buried insulating film 312 formed in the bottom of trenchregion 310, the so-called isolation merged type capacitor configurationcan be achieved and the isolation region can also be used as a regionfor forming a memory cell capacitor. Thus, the capacitance of the memorycell capacitor can be made larger without increasing the array area.

Gate insulating film 304 beneath conductive layer 305, and capacitorinsulating films 308 (308 a, and 308 b) on the bottom and side ofconductive layer 306 may be made of the same insulating film material inthe same thickness. Alternatively, by dual gate insulating film process,they may be formed to have a different film thickness from each other.

Impurity region 302 is electrically connected to conductive layer 320formed of, for example, a first level metal interconnection layerthrough bit line contact BCT. The conductive layer 320 is formed of ametal interconnection layer made of Cu, Al or the like, to constitutebit line BL. Thus, a CUB configuration in which cell plate electrodes CPare present below bit lines BL is achieved.

FIG. 64 is a diagram schematically showing a cross sectionalconfiguration taken along line 62B-62 b in FIG. 62. As shown in FIG. 64,the memory cells (memory cell capacitors; active areas) adjacent to eachother in the row direction are isolated from each other by means ofburied insulating film 312 formed in the bottom of trench region 310.Conductive layer 306 constituting cell plate electrode CP is arrangedcontinuously extending in the row direction. This conductive layer 306includes side wall conductive layer 306 b formed with capacitorinsulating film 308 b interposed in between on the side wall of trenchregion 310; bottom conductive layer 306 b formed contacting buriedinsulating film 312; and planar conductive layer 306 a formed facing,through capacitor insulating film 308 a, to storage node 307 a formed inthe surface of semiconductor substrate area 300.

Therefore, as shown in FIG. 64, the side walls of trench region 310formed at both sides in the row direction of the memory cell capacitorregion can be used as a memory cell capacitor. Thus, the area ofeffective capacitor region MQ is made large so that the capacitance ofthe memory cell capacitor can be made sufficiently large.

In order to form isolation insulating film 312, it is sufficient to usean appropriate process for forming a buried insulating film.

In the above description, conductive layer 305 constitutes a word lineWL. However, this conductive layer 305 may constitute sub word line in ahierarchical word line configuration. In this configuration, main wordlines are formed as an even upper layer of, for example, a second metalinterconnection layer.

[Modification]

FIG. 65 is a diagram schematically showing a layout of a modification ofthe fifteenth embodiment of the present invention. In FIG. 65, cellplate electrodes CP are separately arranged corresponding to word lines(sub word lines) WL0-WL3. Therefore, cell plate electrodes CP0-CP3 eachare arranged commonly to memory cells in one row. The cell plateelectrodes in adjacent rows are separated from each other. Otherelements are the same as in the layout shown in FIG. 62. The samereference numerals are attached to the corresponding elements, anddetailed description thereof is omitted.

FIG. 66 is a diagram schematically showing a cross sectional structuretaken along line 65A-65A in FIG. 65. If the cell plate electrode isformed on the surface of buried insulating film 312 in FIG. 66,conductive layers 306 b formed on the side walls of trench regions 310are isolated from each other by means of buried insulating film 312.Other elements in this memory cell configuration are the same as in thelayout shown in FIG. 63. The same reference numerals are attached to thecorresponding elements, and detailed description thereof is omitted.

The cross sectional structure of this cell plate electrode CP takenalong the word line direction is the same as shown in FIG. 60.

For the manufacturing step of forming the conductive layer constitutingcell plate electrode CP only on the side walls of trench region 310 butnot forming the conductive layer constituting cell plate electrode CP inthe bottoms of trench region 310, for example, the following steps canbe used: a step of forming conductive layer 306 (306 c) on isolationinsulating film 312 in the same way as in the memory cell configurationas shown in FIG. 63, and a step of applying anisotropic etching (RIE;reactive ion etching) to remove conductive layer 306 c in the bottom ofthe trench.

As shown in FIG. 66, by extending cell plate electrode CP on side wallsof trench region 310 inside trench region 310 and exposing the surfaceof buried insulating film 312 without forming any conductive layer inthe bottom of trench regions 310, the cell plate electrodes adjacent toeach other can easily be isolated. Thus, the isolation merged typecapacitor configuration can be achieved and cell plate electrodes CP canbe arranged corresponding to the respective word lines (sub word lines).

In the above-mentioned memory cell configuration, the N channel MOStransistors (insulated gate type field effect transistors) are used asaccess transistors. However, P channel MOS transistors may be used forthe access transistors.

The configuration, in which buried insulating film 312 in the trenchregion is used to isolate the memory cells and the side walls of thistrench region are used as a capacitor, can be applied to theconfigurations of the first to fourteenth embodiments. The isolationmerged type capacitor configuration utilizing the side wall of thetrench region as a memory cell capacitor can also be applied to aconfiguration in which cell plate voltage VCP is controlled for eachcell plate electrode.

In the case that a trench isolation configuration is used for isolatingwell regions or elements in a logic, trenches for isolating memory cells(active areas) may be simultaneously formed in the step of forming theisolating trenches in this logic. By simultaneous formation of thetrenches for forming the capacitors with the formation of the isolatingtrenches in the logic in the same steps, the logic and the memory can beformed in the same manufacturing steps without an increase inmanufacturing steps.

As described above, according to the fifteenth embodiment of the presentinvention, in the configuration in which memory cells are isolated bymeans of buried insulating film in the bottom of trench regions, theside walls of the trench regions are used as memory cell capacitors toachieve isolation merged type capacitors. Thus, a memory cell capacitoroccupying only a small area and having a large capacitance can beimplemented.

OTHER EMBODIMENTS

As the configuration of word lines, the hierarchical word lineconfiguration of a main word line and sub word lines is not used but aword line shunt configuration, in which a polysilicon word line isshunted with low-resistance metal interconnection line, may be used. Acombination of the hierarchical word line configuration and the wordline shunt configuration may be used.

As the memory cell transistors, P channel MOS transistors may be usedinstead of the N channel MOS transistors.

As the memory cell capacitors, the planar capacitors are used. However,in the case that a trench isolation configuration is used in the logic,trench capacitors may be used as the memory cell capacitors. An increasein manufacturing process steps for forming the memory cell capacitorscan be suppressed by forming trenches in the memory cells simultaneouslywith formation of the isolation trenches in the logic section.

As described above, according to the present invention, cell plateelectrodes and word lines of memory cell capacitors are formed in thesame interconnection layer, and memory cells are simultaneouslyconnected to bit lines in a pair. Thus, additional manufacturing processsteps for forming the memory cell capacitors can be made unnecessary.Logic and embedded semiconductor memory device can be formed by the samemanufacturing processes. Moreover, a semiconductor memory devicesuperior in data retention characteristics can be achieved. Furthermore,the height of the memory capacitors can be made low so that the stepbetween the memory array section and the peripheral section thereof canbe decreased.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A semiconductor memory device, comprising: a plurality of memorycells arranged in rows and columns, each of said memory cells includinga capacitor including a cell plate electrode and a storage electrodearranged facing to said cell plate electrode, for accumulating electriccharges corresponding to storage data, each memory cell beingelectrically isolated from adjacent memory cells thereto by means of atrench insulating film formed in a bottom of a cell isolating region ofa trench structure, and each cell plate electrode comprising (i) a firstelectrode layer formed at least on a side wall of the trench and (ii) asecond electrode layer formed above said trench insulating film andelectrically connected to the first electrode layer formed on said sidewall, said storage electrode being formed at a surface of asemiconductor region and facing to said cell plate electrode with acapacitor insulating film laid in between and being isolated from thestorage electrode of an adjacent memory cell by means of the trenchinsulating film, and the trench being formed in said semiconductorregion; a plurality of word lines arranged corresponding to the rows ofmemory cells and each connecting to the memory cells in a correspondingrow, said word lines being formed in a same interconnection layer as thecell plate electrodes; a plurality of bit lines arranged correspondingto the columns of memory cells and each connecting to the memory cellson a corresponding column, the bit lines being arranged in pairs; androw selecting circuitry for selecting an addressed word line out of theword lines in accordance with an address signal, the memory cells beingarranged such that data in selected memory cells on an addressed row aresimultaneously read out onto bit lines in a pair by a selected wordline.
 2. The semiconductor memory device according to claim 1, whereinthe cell plate electrode is arranged, commonly to the memory cellsarranged in two rows, extending in a row direction.
 3. A semiconductormemory device, comprising: a plurality of memory cells arranged in rowsand columns, each of said memory cells including a capacitor including acell plate electrode and a storage electrode arranged facing to saidcell plate electrode, for accumulating electric charges corresponding tostorage data, each memory cell being electrically isolated from adjacentmemory cells thereto by means of a trench insulating film formed in abottom of a cell isolating region of a trench structure, and each cellplate electrode comprising an electrode layer formed, at least on a sidewall of the trench, (1) being electrically isolated from the electrodelayer formed on another side wall opposite in a column direction of thetrench by means of said trench isolating film, and (2) extending in arow direction, said storage electrode being formed at a surface of asemiconductor region and facing to said cell plate electrode with acapacitor insulating film laid in between, and the trench being formedin said semiconductor region; a plurality of word lines arrangedcorresponding to the rows of memory cells and each connecting to thememory cells in a corresponding row, said word lines being formed in asame interconnection layer as the cell plate electrodes; a plurality ofbit lines arranged corresponding to the columns of memory cells and eachconnecting to the memory cells on a corresponding column, the bit linesbeing arranged in pairs; and row selecting circuitry for selecting anaddressed word line out of the word lines in accordance with an addresssignal, the memory cells being arranged such that data in selectedmemory cells on an addressed row are simultaneously read out onto bitlines in a pair by a selected word line.
 4. The semiconductor memorydevice according to claim 3, wherein the cell plate electrode isseparately arranged corresponding to each respective row of the memorycells.